Two things that I've heard repeatedly are that 1) Chrysler didn't keep records broken down by color, and 2) many records that did exist were lost in a warehouse fire. I've asked a lot of people about the second point, and I've never found anyone who could verify that. I'm inclined to believe it, but to "really believe" it I'd want to hear something like the name of the warehouse or where it was located.
There are a lot of production numbers out there that don't agree with one another. I'm not certain, but I think a lot of them come from current numbers remaining and verified, and then extrapolated as a percentage to total production, which wouldn't be scientific, but would be a starting point.