color spaces and representation (#1572)

`Color` can now be from different color spaces or representation:
- sRGB
- linear RGB
- HSL

This fixes #1193 by allowing the creation of const colors of all types, and writing it to the linear RGB color space for rendering.

I went with an enum after trying with two different types (`Color` and `LinearColor`) to be able to use the different variants in all place where a `Color` is expected.

I also added the HLS representation because:
- I like it
- it's useful for some case, see example `contributors`: I can just change the saturation and lightness while keeping the hue of the color
- I think adding another variant not using `red`, `green`, `blue` makes it clearer there are differences

Co-authored-by: Carter Anderson <[email protected]>

Author: mockersf