Thanks for the file. I've taken a look at a single car and it would appear the the paint colour is OK. The variations between them were quire tough to see so I added some more vibrant colours for testing purposes and all seemed OK.
Hope that helps,
I can't get this to work, I've removed all the other cars in the RC definition, except for one, I tried to replace the Railclone color map as well (with bright colors). I tried with Vraycolors instead of using the color swatch. It justs ignores the other colors/maps/swatches. It only takes the first one. No idea why it works in your case and not mine. Maybe there's a bug with this RC beta?
EDIT: I just updated my RC to the latest Beta, and it seems it's working now. Not sure if it was because the update or because (as Realviz stated as well) I had to close and reopen Max for it to work. Although this is unlikely as I closed and reopened Max a few times in the mean time.