Inside, check new oil colour (6)
I believe the answer is:
violet
'colour' is the definition.
(I know that violet is a type of purple)
'inside check new oil' is the wordplay.
'inside' is an insertion indicator.
'check' becomes 'vet' (to vet someone is to check their background).
'new' indicates an anagram.
'oil' with letters rearranged gives 'iol'.
'vet' placed around 'iol' is 'VIOLET'.
(Other definitions for violet that I've seen before include "Purplish colour" , "Girl's name - colour" , "Seldom" , "plant" , "Rainbow colour; flower" .)