Painting that’s sea-blue? (11)
I believe the answer is:
watercolour
'painting' is the definition.
(I know that watercolour is a type of painting)
'sea-blue?' is the wordplay.
I cannot quite see how this works, but
'blue?' could be 'colour' (blue is a kind of colour) and 'colour' is found in the answer.
The remaining letters 'water' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for watercolour that I've seen before include "Type of painting" , "Painted picture" .)