Shell ought to be red not black, curved further up (5-10)
I believe the answer is:
round-shouldered
'curved further up' is the definition.
(with curved shoulders)
'shell ought to be red not black' is the wordplay.
'shell' becomes 'round' (as in ammunition).
'ought to' becomes 'should' ('you ought to' means 'you should').
'not' suggests deleting specific letters.
'black' becomes 'b' (as in pencil classifications).
'be'+'red'='bered'
'bered' with 'b' removed is 'ered'.
'round'+'should'+'ered'='ROUND-SHOULDERED'
(Other definitions for round-shouldered that I've seen before include "appearing to slump?" , "poor posture" , "With a curved upper back" .)