Carry on designing stripes (7)
I believe the answer is:
persist
'carry on' is the definition.
(to persist is to carry on with something)
'designing stripes' is the wordplay.
'designing' indicates an anagram.
'stripes' anagrammed gives 'PERSIST'.
(Other definitions for persist that I've seen before include "Continue in spite of difficulty" , "Stripes (anag)" , "Pursue course doggedly" , "Abide" , "Keep going" .)