Borders in study, a deep red (7)
I believe the answer is:
crimson
'a deep red' is the definition.
('crimson' can be a synonym of 'deep red')
'borders in study' is the wordplay.
'borders' becomes 'rims' (I've seen this in other clues).
'in' is an insertion indicator.
'study' becomes 'con' (I've seen this before).
'rims' inserted inside 'con' is 'CRIMSON'.
(Other definitions for crimson that I've seen before include "Vivid red" , "Colour of deep blushing?" , "Become red-faced" , "Looking embarrassed" , "Deep red colour" .)