I am assuming it was an upchuck type stain? Unfortunately the dyes they use in cat food result in hairballs that leave stains that don't ever seem to come out. I disgusting mix of yellowy bile from kitties tummy and then whatever it is they put in the cat food. You can probably fade it with another wash or two. You can try Grandmas secret spot remover. It is sold loads of places, like JoAnns and on line.
Let us know if you are successful. I never was.