I had the same problem with all my sps corals that have yellow color, until I brought phosphate and nitrate down to 0, they all got back to their true color.
Everything that I have read suggests not to run an SPS tank at these levels and that a trace of nitrate and phosphate is required to maintain sps corals.
Normally my brown corals go through a green phase before coloring up
I run an ATI 8x54W Sunpower Dimmable.
A lot of the corals were given to me browned out ( I don't know what colour morph they were originally ).
Others, and I will pick out a red abrotinoides, has morphed into a metallic green.
All various different hues of green...but all green. They all grow well though.
It's good to know that, now I don't need to worry too much about nitrate and phosphate.
Nah, I'm leaving be at the moment.
The only thing I have added recently ( a week ago ) was a phos reactor.