It was supposed to be Red 3, but I had a painting mishap that resulted in paint that would not cure (Model Master, I'd never had a problem with it ever before), I think there was some turpenoid contamination from another project. So, instead of scrapping it, sections were sanded back and this instead became a test bed of sorts. I was experimenting on opacity levels from the airbrush and seeing if I could get tonal variations through one color by the underlying colors.
You can almost make out the variation in the orange from the yellow, camo gray, and green that are underneath. Can see it more in person than in the photo though.