Lead in paint Rothko has absorbed (5)
I believe the answer is:
intro
'lead' is the definition.
(I've seen this before)
'in paint rothko has absorbed' is the wordplay.
'has absorbed' says the answer is hidden in the clue.
'INTRO' is hidden within 'in paint rothko'.
(Other definitions for intro that I've seen before include "One starts" , "Musical opening" , "this may get one started" , "Lead" , "Opening bars to a piece of popular music" .)