Support for custom colorschemes

Many people have issues with their colorscheme hurting the gameplay.
Common issues include:
- People using pywal --> colors become completely meaningless
- People using light-themes --> cannot see white lines on the empty background, because their background color is also white

There would be multiple solutions for this:
- Provide a way to configure custom color-palettes
-> issue here: Doesn't really fix the light-theme issue
- Always use the same palette for everyone, hard-coding the palette in 256color / Truecolor
-> issue here: what palette? light/dark?
- To fix the light/dark theme issue: always set the background of the canvas to a fixed color

Start by reviewing the issue's three proposed approaches for custom palettes and fixed canvas backgrounds. Inspect the color-rendering entry points and determine which approach resolves both pywal or light-theme conflicts. Done means the selected behavior supports usable gameplay across custom terminal colorschemes.

Written by the indexing model from the issue text.