Slip into some red ones (3)
I believe the answer is:
don
'slip into' is the definition.
(I've seen this before)
'some red ones' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'DON' is hidden within 'red ones'.
(Other definitions for don that I've seen before include "Put on clothes like noss" , "Yorkshire river" , "Slip into" , "Spanish male title" , "Put on the learned man" .)