I know the colour of MkIV TDI, TDI, TDI badges reflected the 110, 130 and 150ps.

What were the equivalent for the GTI?

The red 'I' used to stand for the turbocharged version, as apposed to NA

Ah, well I'm even more happy with my car then;)

Just depends.........The letters and badges get swapped all the time! If you have a Proper GTI it'll have a 1.8T motor, if you have a fake one It'll either have a 1.8 20V NA Motor or the later ones have the Old 2 litre motor! Think later on in the MK4's life the Fake GTI's were badged as 2.0!