Thanks for all the comments guys.
Confession time, the rear bumper has no white paint on it, it's just a trick of the light - **cough** *ahem** However, it might be something I'll try on a future build!
Peter, the underside is finished with Tamiya enamels - semi gloss black (frame), gloss black (rear end and front suspension), gunmetal (rear springs), flat aluminium (transmission pan) and titanium gold (sump). Transmission, sway bars, exhaust are Citadel/Warhammer Boltgun metal. All brush painted. Thanks for asking, hope this helps.