Clean up color logic in contributors.rs example

[alice-i-cecile]

Nit for future PR: This looks gross. I think it would look nicer to declare const: SELECTED: Hsla = Hsla::new(0., 0.3, 0.2, 0.92); and then use SELECTED.with_hue(hue).into().

Originally posted by @bushrat011899 in #12163 (comment)

[rparrett]

I had a half-baked branch with some other improvements that I re-did on top of the new color changes and included that change.

https://github.com/bevyengine/bevy/compare/main...rparrett:bevy:contributors-improvements-main?expand=1

I'll PR that when color stuff settles down unless someone else gets to it first.