No, there wasn't a G4 90 used on the challenge.
For the 2003 event they had Freelander, Disco II, Range Rover and 110.
For 2006 they had Freelander, Disco 3, Range Rover, RRS and 110.
They did make a 90, and a 110, G4 LE version which was never used on the event, that came in
Java Black,
Borrego Yellow,
Zambezi Silver or
Tangiers Orange.
For more info have a look at the
G4 Owners Club