He is a vibrant red usually.
The light wasn't too good in this photo, but he is still a nice bright red.
It's just the piece missing from his tail which is unusual.
Okay
Have you checked your water paras? If so, could you put up the results? Also, do you have anything sharp in the aquarium he could have caught it on?
I'm sure betta's sometimes nip their own tail, Mines never but i'm sure i read it on here that some do. doesn't look infected though so will grow back in time