Morphing Green Texas

We have two Texas' in our tank which were the same size/shape/colour when they went in 6 weeks ago. In that time, they have both grown significantly, but one has changed dramatically. It has developed somewhat of a nuchal hump, as well as a dark colouration (blue/black) on it's underside, from his mouth to his anal fin mainly. Some other dark colourations have also occured. It's overall bulk has increased to the point where it is noticably larger than the other.

We are curious as to what this could be, though we are also unsure of sexing differences between Texas cichlids. Another point of interest is that we medicated the tank to eradicate some white spot 9 days ago. The white spot has been eradicated using Malachite Green. We have ceased using the medication (about 4 days ago) and conducted a 50% water change since (about two days ago). We noticed the colour change during the medication process. The two may be unrelated, but we are generally curious as to whether Texas naturally change like this. The morphing Texas is about 3 inches long.

Cheers.