ALL metallics have this issue: CGM, RJT, SIM, IOM, IBM, ABM and SGM.
It's more pronounced in the bright sun and from certain angles. See the many other links on this subject. The plastic parts (bumpers and fuel door) are painted at a different location than the robots which paint the steel body. The paint is a different compound because paint on plastic has to be allowed to flex or it will crack.
For the solids, only white seems to have a discoloration issue. The rest seem ok... BLK, VR and RY.
My Theory:
Since other manufacturers don't have this issue as much, I can only conclude that the issue is in GM's process: the amount of metallic flake is not the same between the two painting locations. In CGM for example, there are two different colors of flake. If the two painting locations don't have exactly the same number of flakes per color per drop of paint, there will be a noticeable difference. The more metal per drop of paint, the lighter the shade because it reflects more light. Also, the metallic flake, when hitting the elecro charged steel body of the Camaro, will not align in the same direction as the flake when applied to a non-charged plastic piece. The subtle difference would then be visible in the sun from different angles. This assumes that the individual flakes are not round balls of steel, but rather elongated shavings which react to electormagnetc fields like a compass. Again, just a theory, but I think it holds.
Some mis-match examples:
Fuel door:
Bumper and fuel door:
At least GM is consistent...all cars of the same color have the same degree of problem.
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