My Tilapia Turns Black! Nice!

My friend Felix and I caught several Tilapia (a.k.a. Japanese Fish possibly a Oreochromis niloticus about one month back. I am not quite sure if it's the right name but at first all of them is silver Grey color in my fish tank.

Now, one of them turning in a stunning BLACK color with pink tail.

I read about the male Tilapia will turn black when they are going to mating!! So I may get babies! LOL I think my 2 feet tank is not big enough!!