User blog comment:That Lamborghini Guy/Pegasus Vehicle Colours/@comment-4210063-20160112220748

Pegasus vehicles spawn with the vehicle's default colors. Insurgent Pick-Up and Mule can spawn with more colors (afaik Mule can spawn in black, and I got a bunch of sandy brown Insurgents before). The other two have only one default color.

Any vehicle colors other than the default are Special Vehicles (unique colors) which are not intended to ever spawn in free gameplay (sometimes there are exceptions to that like the NPC modified vehicles in V or Vincenzo's Kuruma in LCS).