Pink substance to see in the mouth? (5)
I believe the answer is:
coral
'pink' is the definition.
(coral is a shade of pink)
'substance to see in the mouth?' is the wordplay.
'substance' becomes 'c' (C is an example).
'to see in the mouth?' becomes 'oral' (I've seen this in another clue).
'c'+'oral'='CORAL'
(Other definitions for coral that I've seen before include "Pinkish-orange colour" , "Marine polyps, often forms reefs" , "Deep pink colour" , "Basis of reefs" , "Tiny animal forming reef" .)