Alpha channel

Can we create a Color class with an Alpha channel? Maybe call it ColorAlpha or something like that?
We can also create a GetColorAlpha and SetColorAlpha to use the alpha channel.
This might also mean we need to create overloads for all other functions using Color, like DrawLine.

Start by locating the existing Color class, GetColor/SetColor functions, and DrawLine entry point. Clarify whether alpha belongs in a new Color type or the existing API, then enumerate the Color-based functions that need compatible overloads and define the expected alpha behavior.

Written by the indexing model from the issue text.