Hi roving_bovine.
First up, you should have posted this in the
iMac & eMac Forum not the PowerMac forum, but you live and learn and all that
Anyway, the background behind the Mac OS 9 startup screen is actually a bunch of black and white dots in a checkerboard pattern. This looks llike gray most of the time, but at certain resolutions, on a curved screen like the G3 iMac's, the image can get distorted. This can look like a number of things, usually just strange patterns on the screen, but can also look like various colours.
If your screen looks fine once the computer is started (and on the screen where the desktop is behind the Mac OS 9 logo, and the extensions are dancing along the bottom of the screen), there's probably nothing to worry about.
- proton