I believe that is a Framework mod. If someone doesn't have it already modified in their rom... then you have to learn how to mod the framework file. Theming takes time, but it's worth it in the long run.
OK golum. Use metamorph to easily theme any icon you want. Go to droidpirate.com to get icons and follow directions and youll be good. Super easy on froyo. I've had trouble on gb, but i heard Ninjamorph works on 2.3 so check the forums, youtube and of course google
Btw im on gb rooted, TBH one I think, and really didn't have many problems with metamorph. changing my batt icon was smooth. Changing my notification bar color always went to force close. pulled the battery, reboot and the color was there. Did that about 10 times til I decided black was it. Hopefully that didnt build up some chode somewhere.... Now I've got a blue market. I'm loving this stuff.
My girl and her white iphone are sick of me saying, "look what I did."