Not meaning to be controversial, but i really feel stongly against keeping bettas in this size tank alone...
The reason i say this is because i've had, and heard of many bettas going "mad" and eating their own tails (presumed due to boredom and lack of entertainment) the only time i feel something like this is acceptable, IMO, is when there is another betta nearby for flaring matches to keep the betta occupied...
But, he is a lovely looking betta and he does indeed match the gravel nicely, but please if you do have a bigger tank, move him...
N.B. This is not meant to cause offese i'm just expressing my opinion