Here's a pic of the greenest male ghost that I have raised.
I've found that keeping them in a humid and well lit space increases the probability of ghosts becoming greener in color. I think my favorite colored mantis was a female and dark brown when I acquired her. I kept her near a window where she would get a few hours of sun in the morning a stayed well lit throughout the rest of the day. I can't remember if she was sub-adult or pre sub-adult when I got her but when she molted to adult she was a really beautiful combination of brown, tan, and green. It was awesome!