Corals becoming pastel color?

[MarkoD]

I've noticed over the last month my corals have started turning a pastel version of their colors.

what would cause this?

calcium is a 430

alk is 8dkh

magnesium is about 1300

phosphates .02 (basically where they've always been)
nitrates: undetectable.

seems to be happening to all kinds of corals (sps, lps, zoas) and colors (reds, blues, purples)

only green seems to be maintaing color