Dull coloured, hard-centred persimmon (5)
I believe the answer is:
khaki
'dull coloured' is the definition.
(khaki is a dull colour)
'hard-centred persimmon' is the wordplay.
I cannot really see how this works, but
'hard' could be 'h' (abbreviation used in pencil classifications) and 'h' is found within the answer.
'persimmon' could be 'kaki' (kaki is a kind of persimmon) and 'kaki' is found in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for khaki that I've seen before include "'Colour, often used for military uniforms (5)'" , "Dullish brown colour" , "Brownish-yellow" , "buff" , "Military uniform cloth - colour" .)