Hi sandy and welcome to the forum.
A lot of red bettas have silver face coloring so Frodo's coloring could be completely natural. However, I'm just a little concerned that they might be ammonia burns because his water isn't changed quite as frequently as it should be. In what is basically a 1 gallon tank because you only put 1 gallon in, you need to change 50-100% of the water every other day for him to stay healthy. Bettas excrete ammonia through their gills as part of their waste. Only problem is ammonia is highly toxic to them so in a small volume of water, that ammonia builds up really fast and begins to burn them. If left untreated, these burns could lead to bacterial infections. The only way to keep the ammonia level down is to change the water frequently.
Is Frodo acting any differently? Is he acting lethargic and does he stay at the bottom a lot? Does he look bloated in any way? Has he stopped eating?
If you could answer those questions, that would really help us tell if Frodo's silvery cheeks are normal or a sign of illness.