When is the instar that I can tell my mantis' gender?

I have two Carolina mantis at instar 4. And, if I put in more green vegetation, can the mantids change color once they molt again? I can't seem to find specific information about that particular species.

You can sex them at any L stage
Although it's kind of hard when they're a smaller sp.
&
Are like ant size or smaller than a fruit fly when they hatch out

Kind of hard to tell from the pic so guessing here
But would say the one in the 2nd pic looks like it's a female

If you can take clearer shots of their bellies I should be able to sex them for you
Or
Just count the segments on their abdomens
The females will have 6 & the males will have 8
Males always have more than females

Pics are of my adult female & sub adult male P. Griffinii / Griffin Mantis pair
But it's the same with Carolina

1st pic is of the female & the 2nd one is of the male

Even though the color of their surroundings can effect their color
It's not always a factor
Some are just the color they are & will stay that color no matter what

If I have two mantids of the same gender, is there a place to obtain a mature mantis that is the other gender?