the pink is used a transparent color, so anything pink will be transparent on the player - solid pink though, not a true alpha channel at all, so no fading blends into the pink or it wont work, and images are supposed to be 32 bit BMP images, but 24 should be ok
have a wizz at this site for ipod themes, they come with full sets of png icons you can adapt and use, maybe
http://www.ipod-touch-themes.de/
remember to post your end results
good luck
and BTW dont be put off by all the images in the firmware, rockchip are seriously bad at housekeeping and 50% of the images are for other players UI`s!!!!!