[Feature Request]: Add possibility to change colors.

Hello! I have a little problem when I'm using `redshift`. I'm almost not able to see the elements when redshift is activated. <br>
It would be awesome if you could add something like a sidebar where the user could set the starting color value to display the colors. <br>
## How to reproduce ##
Start redshift with the following args:
```bash
reshift -O 1000
```
and than start elements.