I generally agree w/Kisara, tho I doubt that it involved each Colt employee[:D].
Basically, Colt started out w/ the lightest of their colors on the SP1 series, and most SP1s are pretty much the same color. The problems started when Colt went beyond the SP1s. They apparently started the later prebans pretty much the same color. My own SP1 has a later forward assist big hole upper on it, and even tho the upper is at least 10-12 years newer, it's essentially the same shade as the early lower. Then they started mixing and matching parts from different production runs, and you got mismatched colors on uppers and lowers; and even when the two were color matched, you couldn't necessarily predict which shade they might be.
I've seen little or no evidence that label color played any part in this; except that , the later the label, the more likely (but not certainly) a darker color. Early specimens of a later color label were quite likely to be more or less the same color as the later pieces of the previous run.
Frustrating, ain't it?