Hi, My Husband Has Diabetes And Has Had It Under

Hi, My husband has diabetes and has had it under control through medication. He has developed what looked like a blister on the side of his big toe. We thought it was from a new pair of boots. It does not hurt but it is not going away and his surrounding toe area is red and the immediate area around the blister is white. I'm concerned it is more then a blister. He has feeling in the toe and in the area of the blister. It looks like it should hurt but it does not.