do they spit out EACH flake? if they do, it could be bacteria in their throats, signaling an internal bacterial infection.

   does each individual fish spit out one or two types(colors) of flake but accept the others? maybe it is just individual taste.

  or, does the whole tank reject a certain color? my first year with mollies, the entire tank rejected the red flakes. they ate the others, though.

   if they spit out all of the flakes, it could also be that your flake food has gone bad and you need a knew container. give that a try. if they are still rejecting each flake, it's most likely a disease.

  maybe you could try crushing your flakes into smaller peices before feeding. try to feed the same amount even with this method though. sometimes my fish will spit out a flake that they think is too big but they eat the smaller ones.