Sun's red, doctor! Strip! (7)
I believe the answer is:
undress
'strip' is the definition.
(I know that strip can be written as undress)
'sun's red doctor' is the wordplay.
'doctor' is an anagram indicator.
'suns'+'red'='sunsred'
'sunsred' anagrammed gives 'UNDRESS'.
(Other definitions for undress that I've seen before include "Remove one's clothes" , "Take off clothing, strip" , "Remove clothes, strip" , "Take one's clothes off" , "Nudity" .)