I assume you have chosen the color display mode.  Otherwise, no colors will be shown at all.

In the current version of BikeCAD, if you display the auxiliary view of the stays, the rear wheel will automatically appear faint and not in color.  This was done so that the rear wheel wouldn't obscure the detail of the stays.  This will be changing in BikeCAD version 10 which will be available next week.  In version 10, you will be able to choose whether to show the rear wheel in color, faint or not at all.