Purple colored bikes?

If you are talking to a fitter, you can ask them about "women's bikes". I don't believe the differences are significant. Women are frequently shorter than men... so smaller sizes (which is what you need). They may have slightly longer legs and a shorter torso, but I can't see it as making a huge difference at this point. Perhaps the only significant difference would be the width of the seat, so you may need to add a small narrow seat.

Everything will change rapidly with the kid. So, get him "fit" now, and he'll grow taller, longer legs, arms, torso, etc in a year.

Personally I would just eyeball it. Get the seat height set right, & ride. "Test Ride" any bike you buy.