I have an iBook G4 (Late 2004) that I just recently upgraded to Leopard using the 10.5.6 DVD included in the Mac Box Set. Whenever it boots, after the chime the screen stays black until the login screen. This happened occasionally with Tiger, but I found a post somewhere where someone suggested to hold the power button while powering on until you hear a beep. That solved it in Tiger, but I have not once seen a grey Apple screen in Leopard. I forgot to mention that I have reset the PRAM and PMU.