tim, though I can't say for sure, my guess would be that the other colored coins were less complicated to apply color to, having less angles and isolated areas. Presumably, the end result was better application of color. They weren't perfect though, I remember the poppy being slightly out of the "target", or being splotchy on some coins.
The
RCM is a fairly state of the art mint, to me this is plain shoddy quality control and/or poor manufacturing methods.
I'm really hoping a mule turns up one of these days to spice things up a bit.