4,228,250,625 different colors is overkill.
I'd rather have sliders that work in increments of 32, and the opacity in increments of 64. This way, you'll be able to tell the difference between colors.
Also, the total colors will go from 4,228,250,625 to 2,048. Although, I'd like to see a basic 256 colorset with 4 different levels of opacity. (That's 1,024 colors).