Bottling crude oil, check for colour (6)
I believe the answer is:
violet
'colour' is the definition.
(violet is a kind of colour)
'bottling crude oil check' is the wordplay.
'bottling' indicates putting letters inside (bottling is a kind of containing).
'crude' indicates an anagram.
'check' becomes 'vet' (I've seen this before).
'oil' with letters rearranged gives 'iol'.
'iol' placed inside 'vet' is 'VIOLET'.
'for' is the link.
(Other definitions for violet that I've seen before include "plant" , "Girl's name - colour" , "Bloomer" , "Colour; flower, source of fragrance" , "A flower for a girl" .)