Male kenyi turning black, why?

[MMantelli]

Well you know the question now here's hopefully all the info you need.
Temp 78-80
Ph 7.6-7.8
Ammo 0
No2 0
No3 40
50% water change every sunday, filter has uv sterilizer, I use tap water and prime. I feed NLS Thera+A daily and tetra cichlid flakes a few times a week the day before the water changes I feed frozen foods in the morning then peas in the evening and fast them on the day of the changes.

Now for the fish they all look and act healthy I even had some fuellebornis breed recently. The 2 in question are the only ones that seems to be "looking dirty" the other male kenyis are all bright yellow. And its not like when the gold lab does it it fades in and out they are like this all the time it kind of looks like they got hit with black overspray so to speak. I can't get any good pics but will work on getting a video of the affected fish. If you need more info please let me know. Thanks in advance.

 

[MMantelli]

Here's 2 videos the first one shows the issue a little better the second video shows the affected fish in comparison to the other ones of its kind. The video doesn't show it as bad as it looks in person and sorry about the glares ill try it again after the lights come on tomorrow.

 

[aquandrew]

it looks like hes getting ready to breed. the male that is dominant and about to breed will get dark vertical bars while the rest stay yellow

 

[MMantelli]

I doesn't really show in the video but it not just bars it is almost like his whole body is getting a grayish tint to it does that go along with the darkening of the bars?