Add transparency to wordpress color picker?

Question: How could you add a few transparency options (none, semi-transparent and solid) to the chosen color in the wp color picker?

I’m working on a set of theme options. I am using the wp color picker wheel to select a color for the post backgrounds. A transparency option would fantastic if that is possible.
Thanks

Don’t use the built-in color picker. It is hard to use already and it will be replaced in 3.5 anyway. You will need a custom one to get transparency.