I just prefer them BLUE

"Colorless green ideas sleep furiously" is a sentence composed by Noam Chomsky in 1957 as an example of a sentence with correct grammar (logical form) but semantics which are nonsensical.

At the syntactic level the sentence is OK, however it does not make sense because things logically cannot be colorless and green simultaneously, ideas cannot sleep and nothing can sleep furiously (can it?).

The sentence can be given an interpretation through polysemy. Both green and colorless have figurative meanings, which still make us able to interpret colorless as "nondescript" and green as "immature". So the sentence can be constructed as "nondescript immature ideas have violent nightmares".