diff --git a/DESCRIPTION b/DESCRIPTION
index ab9d683..552bb03 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -28,3 +28,4 @@ Suggests:
 VignetteBuilder: knitr
 LazyLoad: yes
 LazyData: yes
+RoxygenNote: 7.3.1
diff --git a/R/get.colours.R b/R/get.colours.R
index 007d3ff..ec2a873 100644
--- a/R/get.colours.R
+++ b/R/get.colours.R
@@ -1,15 +1,24 @@
 get.colours <- function(
     value.list,
-    return.names = FALSE
+    return.names = FALSE,
+    predetermined.colours = NULL
     ) {
     colours <- grDevices::colors()[grep('(white|gr(a|e)y)', grDevices::colors(), invert = T)];
-    n <- length(unique(value.list));
+    unique.values <- unique(value.list);
+    n <- length(unique.values);
 
     col.list <- sample(colours, n);
+
+    if (!is.null(predetermined.colours) && !is.null(value.list)) {
+        col.list[seq_along(predetermined.colours)] <- predetermined.colours;
+        }
+
     if (is.null(levels(value.list))) {
-        value.list <- factor(value.list, levels = unique(value.list))
+        value.list <- factor(value.list, levels = unique.values);
         }
+
     names(col.list) <- levels(value.list);
+
     if (return.names) {
         return(col.list);
     } else {
@@ -17,6 +26,53 @@ get.colours <- function(
         }
     }
 
+#' Generate a named vector of colors for every value specified,
+#' ordered by the value in `value.order`.
+#'
+#' Assigns colors to values and ensures they follow a specified order.
+#' Any colors specified in `predetermined.colours` are maintained in the order
+#' specified and are used as the first colors for the `value.list`.
+#'
+#' @param value.list A vector of values.
+#' @param value.order An optional vector specifying the order of values. If `NULL`, value order is not gauranteed.
+#' @param predetermined.colours A vector of colors assigned to values. If `NULL`, colors will be generated automatically.
+#'
+#' @return A list containing:
+#' \describe{
+#'   \item{colours}{A named vector of colors assigned to each value.}
+#'   \item{value.order}{The ordered values.}
+#' }
+get.colours.in.order <- function(
+    value.list,
+    value.order = NULL,
+    predetermined.colours = NULL
+    ) {
+
+    if (is.null(predetermined.colours) && is.null(value.order)) {
+        value.list <- NULL;
+        }
+
+    if (is.null(value.order) && !is.null(value.list)) {
+        value.order <- unique(value.list);
+        }
+
+    if (is.null(predetermined.colours) || is.null(value.order)) {
+        predetermined.colours <- NULL;
+    } else {
+        sampled.colours <- get.colours(value.list);
+        sampled.colours[seq_along(predetermined.colours)] <- predetermined.colours;
+        predetermined.colours <- setNames(
+            sampled.colours[seq_along(value.order)],
+            value.order
+            );
+        }
+
+    return(list(
+        colours = predetermined.colours,
+        value.order = value.order
+        ));
+    }
+
 get.colour.luminance <- function(colour) {
     # Formulas and values documented in:
     # https://www.w3.org/WAI/GL/wiki/Relative_luminance
diff --git a/tests/testthat/test-get.colours.R b/tests/testthat/test-get.colours.R
new file mode 100644
index 0000000..237aae7
--- /dev/null
+++ b/tests/testthat/test-get.colours.R
@@ -0,0 +1,225 @@
+expect.character.vector <- function(result) {
+    expect_true(identical(names(result), character(0)));
+    expect_true(identical(result, setNames(character(0), character(0))));
+    expect_equal(length(result), 0);
+    }
+
+test_that('get.colours returns a color for each vector element', {
+  value.list <- c('ABC', 'DEF', 'DEF', 'GHI');
+  colors <- get.colours(value.list);
+  expect_equal(names(colors), c('ABC', 'DEF', 'DEF', 'GHI'));
+  expect_equal(length(colors), 4);
+  for (i in seq_along(colors)) {
+    color.value <- colors[i];
+    expect_true(!is.na(color.value) && nzchar(color.value));
+    }
+  });
+
+test_that('get.colours returns a color for each vector element when return.names is FALSE', {
+  value.list <- c('ABC', 'DEF', 'DEF', 'GHI');
+  colors <- get.colours(value.list, FALSE);
+  expect_equal(names(colors), c('ABC', 'DEF', 'DEF', 'GHI'));
+  expect_equal(length(colors), 4);
+  for (i in seq_along(colors)) {
+    color.value <- colors[i];
+    expect_true(!is.na(color.value) && nzchar(color.value));
+    }
+  });
+
+test_that('get.colours returns a color for unique vector elements when return.names is TRUE', {
+  value.list <- c('ABC', 'DEF', 'DEF', 'GHI');
+  colors <- get.colours(value.list, TRUE);
+  expect_equal(names(colors), c('ABC', 'DEF', 'GHI'));
+  expect_equal(length(colors), 3);
+  unique.colors <- unique(names(colors));
+  for (key in unique.colors) {
+    expect_true(!is.na(colors[key]) && nzchar(colors[key]));
+    }
+  });
+
+test_that('get.colours returns an empty color vector when value.list is empty', {
+  value.list <- c();
+  colors <- get.colours(value.list);
+  expect_true(identical(names(colors), character(0)));
+  expect_true(identical(colors, setNames(character(0), character(0))));
+  expect_equal(length(colors), 0);
+  });
+
+test_that('get.colours returns an empty color vector when value.list is empty and return.names is FALSE', {
+  value.list <- c();
+  colors <- get.colours(value.list, FALSE);
+  expect_true(identical(names(colors), character(0)));
+  expect_true(identical(colors, setNames(character(0), character(0))));
+  expect_equal(length(colors), 0);
+  });
+
+test_that('get.colours returns an empty color vector when value.list is empty and return.names is TRUE', {
+  value.list <- c();
+  colors <- get.colours(value.list, TRUE);
+  expect_true(identical(names(colors), character(0)));
+  expect_true(identical(colors, setNames(character(0), character(0))));
+  expect_equal(length(colors), 0);
+  });
+
+test_that(
+    'get.colours returns expected vectors', {
+        result <- get.colours(NULL, predetermined.colours = NULL);
+        expect.character.vector(result);
+        result <- get.colours(c('ABC', 'DEF'), predetermined.colours = NULL);
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(!is.na(result['ABC']) && nzchar(result['ABC']));
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(NULL, predetermined.colours = c('red','green'));
+        expect.character.vector(result);
+        result <- get.colours(c(), predetermined.colours = c());
+        expect.character.vector(result);
+        result <- get.colours(NULL, predetermined.colours = c());
+        expect.character.vector(result);
+        result <- get.colours(c(), predetermined.colours = NULL);
+        expect.character.vector(result);
+        result <- get.colours(c('ABC', 'DEF'), predetermined.colours = c())
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(!is.na(result['ABC']) && nzchar(result['ABC']));
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(c(), predetermined.colours = c('red', 'green'));
+        expect.character.vector(result);
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c('red','green'));
+        expect_equal(result, c(ABC = 'red', DEF = 'green'));
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c('red'));
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(result['ABC'] == 'red');
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c(NULL,'red'));
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(result['ABC'] == 'red');
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c('red',NULL));
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(result['ABC'] == 'red');
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(c('ABC'), predetermined.colours = c('red','green'));
+        expect_equal(result, c(ABC = 'red'));
+        result <- get.colours(c(NULL,'ABC'), predetermined.colours = c('red','green'));
+        expect_equal(result, c(ABC = 'red'));
+        result <- get.colours(c('ABC',NULL), predetermined.colours = c('red','green'));
+        expect_equal(result, c(ABC = 'red'));
+    });
+
+test_that(
+    'get.colours returns expected vectors with minimum colours specified', {
+        result <- get.colours(NULL, predetermined.colours = NULL)
+        expect.character.vector(result);
+        result <- get.colours(NULL, predetermined.colours = c('red', 'green'))
+        expect.character.vector(result);
+        result <- get.colours(NULL, predetermined.colours = c('red'))
+        expect.character.vector(result);
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c('red', 'green'))
+        expect_equal(result, c(ABC = 'red', DEF = 'green'));
+        result <- get.colours(c('ABC','DEF'), predetermined.colours = c('red'))
+        expect_equal(names(result), c('ABC', 'DEF'));
+        expect_true(result['ABC'] == 'red');
+        expect_true(!is.na(result['DEF']) && nzchar(result['DEF']));
+        result <- get.colours(c('ABC'), predetermined.colours = c('red', 'green'))
+        expect_equal(result, c(ABC = 'red'));
+    });
+
+test_that(
+    'get.colours.in.order returns expected vectors when order is not specified', {
+        # get.colours.in.order has same result as get.colours
+        # with the change that a named list is returned with two members
+        result <- get.colours.in.order(NULL, predetermined.colours = NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c('ABC', 'DEF'), predetermined.colours = NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(NULL, predetermined.colours = c('red','green'))
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c(), predetermined.colours = c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c(), predetermined.colours = NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(NULL, predetermined.colours = c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c('ABC', 'DEF'), predetermined.colours = c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c(), predetermined.colours = c('red', 'green'))
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c('ABC','DEF'), predetermined.colours = c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(ABC = 'red',DEF = 'green'), value.order = c('ABC','DEF'))))
+        result <- get.colours.in.order(c('ABC','DEF'), predetermined.colours = c('red'))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('ABC', 'DEF'))
+        expect_true(result$colours['ABC'] == 'red')
+        expect_true(!is.na(result$colours['DEF']) && nzchar(result$colours['DEF']))
+        expect_equal(result$value.order, c('ABC','DEF'))
+
+        result <- get.colours.in.order(c('ABC','DEF'), predetermined.colours = c(NULL,'red'))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('ABC','DEF'))
+        expect_true(result$colours['ABC'] == 'red')
+        expect_true(!is.na(result$colours['DEF']) && nzchar(result$colours['DEF']))
+        expect_equal(result$value.order, c('ABC','DEF'))
+
+        result <- get.colours.in.order(c('ABC','DEF'), predetermined.colours = c('red',NULL))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('ABC','DEF'))
+        expect_true(result$colours['ABC'] == 'red')
+        expect_true(!is.na(result$colours['DEF']) && nzchar(result$colours['DEF']))
+        expect_equal(result$value.order, c('ABC','DEF'))
+
+        result <- get.colours.in.order(c('ABC'), predetermined.colours = c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(ABC = 'red'), value.order = c('ABC'))))
+        result <- get.colours.in.order(c(NULL,'ABC'), predetermined.colours = c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(ABC = 'red'), value.order = c('ABC'))))
+        result <- get.colours.in.order(c('ABC',NULL), predetermined.colours = c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(ABC = 'red'), value.order = c('ABC'))))
+    });
+
+test_that(
+    'get.colours.in.order returns expected vectors when order is specified', {
+        # get.colours.in.order with order specified
+        result <- get.colours.in.order(NULL, c('DEF','ABC'), NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c('ABC', 'DEF'), c('DEF','ABC'), NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(NULL, predetermined.colours = c('red','green'))
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = NULL)))
+        result <- get.colours.in.order(c(), c('DEF', 'ABC'), c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c(), c('DEF','ABC'), NULL)
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(NULL, c('DEF', 'ABC'), c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c('ABC', 'DEF'), c('DEF', 'ABC'), c())
+        expect_true(setequal(result, list(predetermined.colours = NULL, value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c(), c('DEF','ABC'), c('red', 'green'))
+        expect_true(setequal(result, list(predetermined.colours = c(DEF = 'red',ABC = 'green'), value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c('ABC','DEF'), c('DEF','ABC'), c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(DEF = 'red',ABC = 'green'), value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c('ABC','DEF'), c('DEF','ABC'), c('red'))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('DEF', 'ABC'))
+        expect_true(result$colours['DEF'] == 'red')
+        expect_true(!is.na(result$colours['ABC']) && nzchar(result$colours['ABC']))
+        expect_equal(result$value.order, c('DEF','ABC'))
+
+        result <- get.colours.in.order(c('ABC','DEF'), c('DEF','ABC'), c(NULL,'red'))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('DEF','ABC'))
+        expect_true(result$colours['DEF'] == 'red')
+        expect_true(!is.na(result$colours['ABC']) && nzchar(result$colours['ABC']))
+        expect_equal(result$value.order, c('DEF','ABC'))
+
+        result <- get.colours.in.order(c('ABC','DEF'), c('DEF','ABC'), c('red',NULL))
+        expect_equal(names(result), c('colours', 'value.order'))
+        expect_equal(names(result$colours), c('DEF','ABC'))
+        expect_true(result$colours['DEF'] == 'red')
+        expect_true(!is.na(result$colours['ABC']) && nzchar(result$colours['ABC']))
+        expect_equal(result$value.order, c('DEF','ABC'))
+
+        result <- get.colours.in.order(c('ABC'), c('DEF','ABC'), c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(DEF = 'red',ABC = 'green'), value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c(NULL,'ABC'), c('DEF','ABC'), c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(DEF = 'red',ABC = 'green'), value.order = c('DEF','ABC'))))
+        result <- get.colours.in.order(c('ABC',NULL), c('DEF','ABC'), c('red','green'))
+        expect_true(setequal(result,list(predetermined.colours = c(DEF = 'red',ABC = 'green'), value.order = c('DEF','ABC'))))
+    });