Small Yellow Watchman with faded stripes

[squallius]

Hello,

have a small Yellow Watchman. Bought him in the normal yellow color with the blue dots. Seemed to be stressed out when he entered the tank. 65g reef with docile fish.
During this time, he started to get dark brown/black vertical stripes on the back half of his body. he is happy now, in a symbiotic relationship with a pistol for about the last month.

Is the color normal for a watchman?

Thanks,

Squallius.