... they're all blue.

Denotes offering a choice where there is none.  Either there is literally a lack of alternatives, or all such alternatives are only superficially distinct.

From the PinkFloyd composition of the same name, and--at the time--a phrase commonly used by ad hoc street vendors in Cambridge.  Also, part of a famous (but possibly apocryphal) quote by Henry Ford about the colours available for his Model T car: "Any color you like, as long as it's black."

See also: ClosuresAndObjectsAreEquivalent, FightBetweenGoodAndEvil.