Shade of credibility (3)
I believe the answer is:
red
'shade' is the definition.
(red is a colour or shade)
'of credibility' is the wordplay.
'of' indicates a hidden word.
'RED' is hidden within 'credibility'.
(Other definitions for red that I've seen before include "Colour of Merlot wine" , "- Cross; - admiral" , "Type of wine" , "Bordeaux claret, for instance" , "Flushed" .)