niger color changes

[mortis13]

hello all,

i have noticed that my (5-6 ")niger trigger is changing from his normal blue to a pale almost ice blue and even back through the blue into black sometimes? it only lasts a few seconds and his tail closes up to a point. what is this behaviour? i have recently added an emp angel(3-4"), they seem to get along ok?

 

[sabodish]

mine used to do this as well. from what i remember, stress can change their colors. also, i noticed when it would sleep it would also change colors.