How can you tell which is which when young ?

I had a trio off glades a while back, they are growing nicely but slowly. Getting pink on their necks but still dark heads. They were marked as red racers I think, but with glades I was lucky that I even got the right amount never mind what they are. (another order was for a trio fo reds m/f/f/. ended up with two males !)

This was last year, will get some more pics soon.

Desperate for a female eastern though (and for my male to eat on his own this year)

Mike