Causes for polyp color change in SPS

[tmb22]

I'm wondering if any of you have experience with polyps that change color, given different conditions. For example, the German Blue Polyp acro. This coral can have bright blue polyps, or darker brown polyps (See pictures below). The same exact piece of coral can shift color of their polyps. I'm guessing there are a variety of reasons for this, but maybe high phosphate would cause darker, brown polyps, and a lower phosphate reading would produce lighter, blue polyps?

Any feedback?

Brighter blue polyps:

Darker brown polyps:

 

[g0rilla]

I'm guessing there are a variety of reasons for this, but maybe high phosphate would cause darker, brown polyps, and a lower phosphate reading would produce lighter, blue polyps?

I think you have already figured it out ; )

 

[Tweaked]

Yep, my guess is if you limit the zoox within, the color will show those vivid colors again. Remember, zoox alage is actually brown, and can affect the corals true pigment colors.