Hidden bay, the colour of a sunset? (7)
I believe the answer is:
covered
'hidden' is the definition.
(covering is a kind of hiding)
'bay the colour of a sunset?' is the wordplay.
'bay' becomes 'cove' (I've seen this in another clue).
'the colour of a sunset?' becomes 'red' (a sunset might appear red).
'cove'+'red'='COVERED'
(Other definitions for covered that I've seen before include "Concealed; roofed over" , "Overlaid with something" , "given protection" , "Concealed; dealt with" , "Reported" .)