Maybe make them more opaque instead of completely transparent. They will still be see-through, but will be reflect the unique color of the bubble better.
Transparent Bubbles Icons
This is a fallow up set to my transparent bubbles cursors. Enjoy! I added more colors that I hope more people will like.
P.S. It is difficult to see the full bubble effect unless you view it on a color other than white. Keep this in mind...They just look like a colored ring on white desktops.