Marge Simpson's is blue (4)
I believe the answer is:
hair
'marge simpson's is blue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hair that I've seen before include "Tresses" , "1960s' rock musical with nudity" , "One's crowning glory?" , "Threadlike strands growing from the skin" , "The American Tribal Love-Rock Musical (1967)" .)