When the SSR came down the production line and into paint, the hood, doors, roof panels and tailgate were mounted to the body of the truck. Once through paint, the doors, roof panels and tailgate were sent off site for sub-assembly completion. These parts magically merged back to the production line at just the right point to get attached to the same truck they got painted on.....
External vendors supplied the front and rear fascias, cargo cover, mirrors, windshield pillar covers, tonneau cover and flipper panel to the SSR production line already painted the "standard" colors. As these parts were needed on the production line, they were plucked from racks that had all of the current production colors.....
You will find color variations on almost every SSR for the panels and parts I mentioned. Some variations are really minor (UV, Aqua Blur and Pac Blue are the least noticeable) and others can really stand out. You will notice that some (not all) yellow trucks have a definite difference when it comes to the fascias versus the fenders.
Black is the worst of the bunch. If you really want to see the difference, use a digital camera to take a photo of things that you suspect are different color.
The vendors were held to very tight standards for color match to GM "standards", while the production paint shop was battling with EPA regulations. I was led to believe that the black paint had enough unique problems in the paint shop that they had to limit the number of black trucks they could paint in any one day. Don't know how true it is, but that was one of the things that sticks in my memory.
In case you are wondering why I might know some of this........ I originally had a 2005 Smokin' Asphalt SSR. I purchased it in August of 2005, just before the 2006 came out. I was OK until I had it in direct sunlight and then could not believe the color variation. A couple months of communication with GM resulted in them saying that they would buy back the black SSR. I could either get my money back, or I could pick another truck. We searched all of the local dealers and found that all (five of them) had the same color variation. It was then that we saw the Pacidic Blue for the first time......... It was a "GM assisted trade".....
A trained eye can actually pick put the color variance in certain lights on any of the SSRs. For me, the spot that stands out the most is the meeting point of the cargo cover, tonneau cover and rear fender. If you look carefully at the dealer brochure photo that has the back end of a black truck, you can see the difference between the rear fascia and the rest of the truck.
Hope this sheds a little light on the subject.
Mike