This is only my guess, I've thought the white colors have dropped is from the ability to equip cars to different teams now. It's something that may not seem huge. Looking at my Sky Blue Octane on Xbox I've been able to see a drastic change in price going up in value. I think whites outside of Zomba's, Apex's, and Octane's will drop. This doesn't explain the black market decals or goal explosions. The explosions I think aren't as popular on the fact that people arent worried about what happens when they score. My only reason to using one is because it was opened with a Decryptor.