Bit of the crust a light brown? (4)
I believe the answer is:
ecru
'light brown?' is the definition.
(ecru is a kind of light brown)
'bit of the crust a' is the wordplay.
'bit of' says the answer is hidden in the clue.
'ECRU' is hidden within 'the crust a'.
(Other definitions for ecru that I've seen before include "Greyish-yellow colour" , "Pale, creamy brown" , "Light fawn colour" , "Strange cure for a colour" , "not whiter than white" .)