I can say had experience with the domestic OEs and they will not do special one off colors. I had a customer at Lincoln request a special color on his MKS and they would not do it. He offered $50k and they wouldn't do it. They said that it creates a very valuable car later down the road and that if it ever needed to have the paint matched, it could not be done. I've also heard of GM doing the same. I would be surprised if they did do it.
Now on the other hand, another salesman had a customer trade in his Bentley Arnage with a custom factory paint he paid an extra $75k to get. It was a brown/copper color with beautiful orange/brown leather to set it off!!
GM does do custom colors at the factory. One example is the Mary Kay pink cars with one of the GM paint codes WA590Q. While these are not one off cars they are very limited production vehicles and sold exclusively to Mary Kay. The color listed for this car is Cognac Frost tricoat which is a GM paint color code WA472P. Below is a link to the compnine report for this car so maybe someone else can chime in on this. I believe Saturn had this car painted at the factory this way for the one off charity Sky.
Compnine report for 2007 Saturn Sky in Cognac Frost Tricoat
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