foxface going grey

[e46er]

hey i added a foxface 2 weeks ago he was yellow as could be eating alot very active..
a week ago i started feeding nori with seachem garlic guard and also tried galric xtreme and he seems to go grey and then 15 min later he is yellow as can be and then a few hrs later hes back to grey he never stays grey for more than 5 minutes is this just him being scared? or something else. i just recently starting measuring phosphates 0.25 and am now running a phosphate reactor and carbon in another..
im doing 20 G water changes atleast once a week.
is this mood swings and normal or a very bad sign??