I'm beginning to think the OS paints a rect with the selected background color, then slaps the image on top and lets the background color show through the transparent portion of the image.
That's usually the right way to go. Changing graphics which are already on the screen will sometimes work, but isn't recommended in general and will be actively discouraged as graphics acceleration chips become more common on Palm OS devices. (And as other changes come too which I can't explain quite yet.)
Drawing with transparency on 3.5 was fairly slow, but hopefully that won't affect you. It got lots better in 4.0 and higher.
-David Fedor PalmSource, Inc.
-- For information on using the Palm Developer Forums, or to unsubscribe, please see http://www.palmos.com/dev/support/forums/
