We colour no hard round sort of melon (8)
I believe the answer is:
honeydew
'sort of melon' is the definition.
(I know that honeydew is a type of winter melon)
'we colour no hard round' is the wordplay.
'colour' becomes 'dye' (dyeing is a kind of colouring).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'round' says the letters should be written backwards.
'we'+'dye'+'no'+'h'='wedyenoh'
'wedyenoh' in reverse letter order is 'HONEYDEW'.
(Other definitions for honeydew that I've seen before include "Sweet substance produced by aphids" , "Sweet stuff" , "Melon - Owen Hyde (anag)" , "Food supplied and eaten by 20s (and Kubla Khan?)" , "Type of melon" .)