I’ve decided to separate this issue from my inaccurate model report, as it can be taken care of quicker than it would take to rescan the whole car. This issue has persisted since the first Forza Motorsport on the original Xbox, but it may be done on purpouse. Both the NA1 and NA2 R/Type-R NSXes came from factory in more than just Championship White, which is represented on the NA2 NSX-R, but not the NA1 NSX Type R. The missing NA1 NSX colours are:
Charlotte Green Pearl
Neutron White Pearl
Kaiser Silver
Berlina Black
Sebring Silver
Grand Prix White
Formula Red
Indy Yellow Pearl