Scissortail damsel color change - mating colors?

Surprisingly, I have not been able to find any information via google search on this topic.

I have a tank that I maintain with about a dozen of these

Scissortail damsel - Neopomacentrus bankieri

and 2 of them in particular have changed color somewhat dramatically. Their tails, which are normally yellow, have turned the same color as their body (dark blue) and the back about 1/4 to 1/3 of their body has turned almost white. They are still active and seem healthy. All of these fish have always been ones to hide in the rocks and act somewhat territorial, but the 2 that are colored in this manner seem to now be highly territorial, as if they are guarding eggs. I have not looked very closely to see if I can find any.

Does anyone have any knowledge of mating coloration of these fish? I honestly cannot say that these fish always had yellow tails like the others, which leads me to believe they are the females of the bunch...just a guess, since they are larger and of different coloration