Setting each “color” as a class is straightforward, yes. But changing the transparency (alpha) changes the “color”. If I want three colors, red, blue, orange, I have 3 classes. If I want to set transparency 50 on those, I have to create 3 new classes red50, blue50, orange50.
What I really want to do is have 50 as a separate class so that I can apply it to ANY color.