Clown Trigger Question. please help

I just got home from my LFS with my new Clown Trig,(first one ive had) i floated him for approx 20 min then added some of my water to the bag for about 20 min then caught him and placed him in my tank. i tried feeding him some krill about 5 min after he was in the tank and he ate it all and didnt bother to really share, ive never had a fish do that so quick so i figured he was ok but i noticed when he went under my rocks his black body turned gray? Is this suppose to happpen? I didnt see this at my LFS..will he be ok?
Im so excited!!!! and $160 hit i dont wanna take

My Setup is:
100g with 20g sump
coralife 125 skimmer
rio 3100 return pump
Fish:
1 Niger Trigger 2inch
1 Niger Trigger 4 inch
1 Humu Trigger 3inch
1 Spiny Box Puffer 5inch
1 Tomato Clown 5inch
(new) 1 Clown Trigger 4inch

Thanks

 

fish often lose their colour at night time
makes them less visible to would be predators
It sounds normal to me

Steve

 

kk ya he is acting normal, Thanks for your reply