(Ross is wearing a white suit)
Ross: (to Monica) You like it, right?
Monica: Oh, absolutely. I like it even more on you than I did on Colonel Sanders. Ross, Ross! I'm kidding!
Rachel: Yeah, come here!
Monica: What was it you were gonna tell us?
Rachel: Yeah. Oh, was it how you invented the cotton gin?
Colonel Sanders was the founder of the Kentucky Fried Chicken fast-food chain. He was famous for wearing an all white suit in his TV commercials.
Eli Whitney was the inventor of the cotton gin, and although he is never pictured wearing white, this is likely a joke about the "cottony" look of Ross's suit.