The way Chameleon paint works is it's made up of several layers of paint. The special pigments change color depending on viewing angle. And naturally the brightness of these colors is affected by the lighting.
So when you go about creating a Chameleon paint effect, you want to give surfaces that face the same direction, a similar color. So to use your Z4 as an example, you have a bit of bumper facing forward, and a large part of the side facing towards the camera, and they have the same color. However, they should be different. Getting it right all over the car requires super smooth and precise color blending though, it's really more for very very advanced choppers.
Cant blame a guy for trying though!
Artist formerly known as "Dev"