Switch color constants to RGBA

[pushfoo]

Enhancement request:

What should be added/changed?

• Make all color constants in arcade.color into RGBA constants
• Make all color constants in arcade.csscolor into RGBA constants
• Add a TRANSPARENT_BLACK constant to arcade.color

What would it help with?

1. Provide better immediate-term support for sprite generation with Pillow or drawing into contexts
2. Set the stage for future sprite generation API improvements
3. Make tests for Build improved screenshot API #1342 and other functionality cleaner

This is also a chore einarf and Clepto agreed should be done months ago

[einarf]

I have already made them into RGBA in my branch
https://github.com/pythonarcade/arcade/blob/texture-revamp/arcade/color/__init__.py
https://github.com/pythonarcade/arcade/blob/texture-revamp/arcade/csscolor/__init__.py

[pushfoo]

How long till that gets merged? I'd like to add some more constants to arcade.color and revamp the docstring for arcade.csscolor afterward.

[einarf]

Think we can get away with cherry picking that commit into development. I can look at that a bit later today

[einarf]

#1423