A watercolour? (3,5)
I believe the answer is:
sea green
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for sea green that I've seen before include "Geese ran (anag) - colour" , "Robespierre such an incorruptible (Carlyle)" , "Robespierre's shade" , "Marine colour" .)