There are currently 19 different colors your Vehicle can spawn with; below are the colors available in the game alongside with it's rarity.
Medium Stone Grey - Very Common
Dark Red - Common
Sand Red - Common
Sand Yellow Metallic - Common
Lemon Metallic - Common
Gun Metallic - Common
Earth Orange - Common
Earth Yellow - Common
Brick Yellow - Common
Rust - Common
Really Black - Common
Faded Green - Common
Sand Green - Common
Black Metallic - Common
Dark Grey Metallic - Common
Dark Grey - Common
Silver - Common
Mid Grey - Common
Hot Pink - Very Rare (1 in 500)
This will be updated when further updates on vehicle colors takes place.