[TxMt] Coloured diff display?

I am trying TextMate on two machines, both PPC. One machine displays subversion diffs with colours (the default behaviour, I believe), but the other has plain old black text with white background. I am not aware of having made any selections that should have caused the difference in behaviour between the two machines. I looked in the Preferences -> Fonts and Colors on the machine with no colours in the diffs, and I see nothing that appears to be related to diffs. I moved ~/Library/Preferences/com.macromates.textmate.plist aside and started TextMate again, but the diffs are still monochrome. Where else should I look?

TIA,

Kevin Horton Ottawa, Canada