The explanation given by Helene is the most probable one: The fish are still too young and the female is not ready for laying eggs. If they do not display and the male has no interest in the female by not showing his courtship dance, they are not adult.
The factors you mention – tank, water, food – are quite OK. The new tank is not too wide or too high. Perhaps you will get some mosquito larvae in time, best food for getting the females ripe. I guess that in your old tank you used the same water, so I shall not bother with other parameters which you did not control.
But why did you change the tank at all? There was no necessity for doing so. Helene did not suggest that you should do that. She said rightly “if you were to take one male out”: but there was no reason for doing this. The tank was big enough for a surplus male to hide if necessary. But you did not write of courtship, only of interest of the female for the less dominant male. So I should replace the pair to its former situation and see if the dominant male shows the darker colours again. If it does, this may be induced by the second male more than by the female.
Then you have to wait. Before one of the males selects a cave and tries to get the female in, your fish are too young. Before there is any serious courtship, even spawning in a cave and the male guarding eggs and larvae, there is no need to split the trio. Even then ther maybe no need to do so, because the sub-male has enough room to hide.
Sometimes it’s really difficult to get the female ripe for egg-laying. Therefore be patient and wait. And let the animals choose their partners themselves.