Security left behind, in the pink (10)
I believe the answer is:
collateral
'security' is the definition.
(collateral is a kind of security)
'left behind in the pink' is the wordplay.
'left' becomes 'l' (common abbreviation).
'behind' becomes 'late' (as in behind schedule).
'in the' means one lot of letters goes inside another.
'pink' becomes 'coral' (coral is a shade of pink).
'l'+'late'='llate'
'llate' going into 'coral' is 'COLLATERAL'.
(Other definitions for collateral that I've seen before include "Secondary; parallel" , "Guarantee" , "Confirmatory - recall a lot (anag)" , "Money put up" , "damage?" .)