Auto body repair & detailing: Plastic and metal paiting, painting body, automobile company

Question
Dear sir,
I work in automobile company in India. I was talking on a phone and was looking at one car. Accidently one question raised in my mind that why the body painting (body of car made up of metal) and bumper painting (bumpers made of plastic) differs in quality? We should not able to spot the difference where painted metal part ends and where painted plastic part starts? What is the reason behind this?

Answer
Some colors with a high pearl and/or metallic content will do this. Plastic and metal absorb temperature differently also you have do deal with static electricity. Especially when using tri- colors, most of them have a very high pearl content. Quite often, you can see the difference on a brand new car.