Blush, flush (6)
I believe the answer is:
redden
I believe this is a double definition.
'blush' is the first definition.
(synonyms)
'flush' is the second definition.
(synonyms)
(Other definitions for redden that I've seen before include "Blush or become flushed" , "Evaluate the nature of (something)" , "Reveal embarrassment in colourful way" , "Give visible sign of embarrassment" , "Blush, colour accordingly" .)