WOW, I was just having a problem with this yesterday and poof here's the answer to my delimna. I've been playing with Sal R.'s albumviewer addin trying to get it to work with multiple skins and his buttons are 4 layers of jpgs. Unfortunately, while they look great on day skins they're almost invisible on darker skins. So I figured just put a light image under it and it would work - WRONG. Until I read this thread, I didn't realize I could mix IMG and IXX to get the desired effect. I now use IMG for the button empty and off image while the button down and on images are IXX images. Works a treat!
Thanks for letting me "learn something new everyday."
HARDWARE: Fujitsu Stylistic ST5111w/WiFi and dock, internal Hitachi 500G HD, external 1TB HD, Sierra Wireless Aircard 550, DVD-RW, BoomzBox HD radio, XM Commander, Delorme GPS, Saitek X-52 Pro joystick, BluSoleil Bluetooth, TPMS, FB, Elm327
...Thanks for letting me "learn something new everyday."
I have been struggling to figure out a way to tone down album art in a night skin. Using this as a baseline idea I can get back to work on adding a semi-transparent gray box over the top so white/bright album art isn't so overpowering out on highway drives at night.