how to sex Socolofi's?

Back when I was a serious mbuna-phile, a mentor told me the only way to tell was to hold them upside-down and look at the vent. The female has a bigger one, and either the male or the female has theirs farther from the anal fin. It's been too many years.
Otherwise, have a colony, and let them figure it out.
 
The whole purpose of sexing them is to buy the right mix. Otherwise when I got them.. I got them. I can tell by behavior what they are!

What about the color question? Does the gray turn blue as they mature? or the color is basically as you see it?

Thanks :)
 
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