Wow... I had no idea that it can take them that long to color. I have a tragic story that might explain why I assume that they are both female. I actually bought a trio of them and a male (in my mind the only male) started to color up. Soon after I moved them into the current tank along with a couple nylons full of gravel from the old tank (was trying to help the bio-spira). I neglected to cut off the excess tail of the nylons and the male kenyi swam into one of them and got stuck and died.That said however, at 3.5 inches, there's no guarantee these are both females unless you've vented them to be sure. I've seen males stay blue past 4 inches, particularly if they're not the dominant male in the tank.
I know that the story was completely unrelated but use this is a warning if you plan on putting nylons full of gravel in your tank... CUT OFF THE TAIL END!!! Fish can be curious!
Anyways... back to the point...
Would I be better off if I removed one of them... I really don't want to get rid of both unless I absolutely have to... I like the contrast between them (striped) and the other three species (all solid colors)... plus I'm sorta attached to them after seeing them grow up and all...Keep an eye on the two, it's not usually a good idea to keep only two of the same fish together, even if it is two females.