U can only get cars in their showroom colors, (colors that are available in the game), however the ZZ2 does come in silver. With the ZZ2 in the first slot, use the code,
BodyColor 1C04BC58 - 1456E58A 1C04BC5C - 1456E7A1 Silver Metallic
As far as the Diablo, I can post the codes for it, but U can only get the parts for it, the diablo body is not on the Pal disc, so if U try to get it, U wind up with the body of some small crap box on the Diablo bits. I think some Pal gamers use the Jag body on the Diablo bits.
Lastly, no, just as Famine had mentioned, U can't get individual body parts like spoilers. The bodies are all 1 piece.
DIABLO JGTC(J)
GS2 EU slot 1
CarBase 1C04BC50 - 58FA3545 1C04BC54 - 76FD710B diablo_gt_00
BodyColor 1C04BC58 - 1456EB7F 1C04BC5C - 1456E7A5 1130
CarType 1C04BC60 - 1456E7A5 1C04BC64 - 1456E7A5 Road
brakes 1C04BC68 - 00AE3F2F 1C04BC6C - 7DB46AC2
brake controller 1C04BC70 - 1456F706 1C04BC74 - 1456E7A5
chassis 1C04BC78 - 00AE3F2F 1C04BC7C - 893336C2
engine 1C04BC80 - 00AE3F2F 1C04BC84 - 7D3932C2
drivetrain & VCD 1C04BC88 - 00AE3F2F 1C04BC8C - 7FBA5EC2
suspension 1C04BC98 - 00AE3F2F 1C04BC9C - B7A35CC2
LSD 1C04BCA0 - 00AE3F2F 1C04BCA4 - B33268C2
front tyres 1C04BCA8 - 00AE3F2F 1C04BCAC - 82B85EC2
rear tyres 1C04BCB0 - 00AE3F2F 1C04BCB4 - B8A45EC2