I thought I recall this becoming a thing a decade or so ago, and what was decided was that you could wear colored gloves as long as it's part of your team's color scheme. The Bills, being red and blue are within their rights to wear red gloves. Sucks for KC that they have nothing in their scheme to match up with the Bills blue jerseys.
Denver for instance in this game right now, with an orange and navy scheme, I don't think they're allowed to wear powder blue gloves to try to hide the hands against the Lions, but they can (and are) wearing the navy which is as close as they can get.