Greeny-yellow mucus after wiping top of sleeve (4)
I believe the answer is:
lime
'greeny-yellow' is the definition.
(greeny-yellow colour)
I don't understand the rest of the clue.
(Other definitions for lime that I've seen before include "Caustic calcium" , "Kind of tree or substance used in cement" , "Another name for the linden tree" , "Tree; alkali" , "Green fruit -- green colour" .)