The GCM hens do not have good egg color, the cross does have good egg color. The black one was a pullet. I got rid of the ones that looked like cuckoo marans cockerels, so I probably acted too quickly there.
The hens you got from the cross are proper GCMs, so if you cross the over colored cockeral to the under colored pullets, it will tend to balance it out. Make sure that you keep the lighter double barred males though, ir you'll keep ending up with the darker males and black pullets.