All objects are logically named and have own material of the same name.
There are 4 types of "body" and "saddle" materials.Assign "body2" and "saddle2"(or 3,4) materials to the body and saddle objects to change the colors.

You can see high quality renders: https://zaya.io/fw2c7 

10 geometries(Body,Saddle,tires,...)

Reset Xform

Archive: Max 2015 / obj + mtl / textures.

System units: cm

polys: 854594
verts: 854771

Note: Who works with v-ray version lower than 3.1, pay attention to materials section BDRF (Microfaset GTR (GGX).

The wireframe render shows basic lowpoly topology. The Turbosmooth modifier is not collapsed.