if you know for a fact that you are getting them from a lfs that uses for instance metal halides and you are using t5 or leds I wouldn't mess with your photo periods if everything established in your tank is happy. Restor is a product made to help corals color up and recover from changing light sources.
The corals that look better have a better population of zoox. The corals that are faded in color don't appear to be browning out, looks like more of a tan color that you get from lack of nutrient and or too much light. I see this a lot under LED, and experienced it. I would try to get more of a nitrate level without raising your phosphates further. A supplement like Acropower should be useful for you. You will probably see better PE right away.
Many of your pieces are still small so I would say a bit of patience is required as well
Look at where the brown corals are compared to colorful ones
I have the RS po4 N03 too
Maybe stop using it for at least 2 weeks and see if you have any changes+or_
I hope you get this solved
I had similar experience also concider upping blue Chanel
Make one Change at a time so you can judge