color enhancing or bringing color back

One of my midas changed for the worse IMO. This guy is white bodied with red lips and red finage. Just a few days ago i noticed the back fins edges were starting to turn back and hints of black was on the tail too. Now these few days passed and the black coloring seems to be spreading. There are more black colored areas on the tail and fins. Parts of the lower lip of the midas's mouth is also black too.

What is happening? When i purchased this fish there was not black areas. Am i not giving the needed nutrients to keep the coloring? Or is with midas's they tend to go through stages of morphs, something like flowerhorns? He is currently eating hikari cichlid gold pellets and carnivore stick. A weekly 30% water change.

I want my midas to go back to how he used to look!!!!!!

Though im aware this might be moved but i figured some of the pros can take a look and perhaps give some theories or advice that could help me get back my fish's original coloring.