Neon tetra losing color, no other symptoms
I have a school of 5 neon tetras in my 20 long tank. I about a week ago that one of them has a tanish/pinkish face, and the color faded off the front half of it. It's almost what they look like after the light is turned off all night, but the lights have been on for several hours. There are no other symptoms. It eats, schoals with the others, and is active. I don't see any sort of parasite or abnormalities.
Here's a picture, the affected fish is the top right. It's a bad cell phone pic, sorry.
I'm just a newbie, so if anything I say seems off please call me out on it! Research!