Disappearing blotch

[Captain Bucket]

5" imperator angel, had this guy about 8 months. Seems very healthy except I noticed this faded blotch on his right flank this AM.

Tonight blotch is gone. Any ideas what's up?

 

[Percula9]

Sometimes skin loses its color temporarily. From the picture eveything looks okay. I've seen this before. Stress can cause it.