Green mandarin turning white

There have been a couple different occasions when our green mandarinfish has turned white and froze where it was. the first time we thought it was dead and then it started to move and swim like normal. it happened right after returning home from being gone for 3 days. we figured it would be fine because our tank has plenty of pods for it to eat. we left the light off the whole time. when we got home i turned the light on to check on him and he was white and not moving... we were about to take it out and flush it when it suddenly got its color back and started swimming as if nothing happened. the next time it appeared to but stuck under a piece of live rock so my husband reached in and lifted the rock to make sure it could get out and that it wasn't dead then it turned white again and froze and stayed that way for about 10 hours. only flapping his fins every now and again. (this was yesterday) and today he is just fine swimming around again like nothing happened... it's so weird, has anyone else experienced this with their green mandarinfish? we asked one of our friends that has one and he has never seen his do it. is it something we should be concerned about?
I don't notice it all the time with my mandarin either. Maybe it's hit or miss? But I don't think it's anything to worry about.
didnt made my pod pile yet but yes mine get live brine shrimp it only make it fat but not that healthy

brine shrimp = Candy bar

Mysis Shrimp = Milk
i use some enriched brine shrimp as well as cyclop-eze formula 1 pelets and a copapod additve liquid thing
my mandarin swims up into the column and eats its kinda cool to watch