The guys outside left an open inkpot with a darkish pigment (7)
I believe the answer is:
melanin
'pigment' is the definition.
(melanin is a kind of pigment)
'the guys outside left an open inkpot with a darkish' is the wordplay.
I cannot quite see how this works, but
'left' could be 'l' (common abbreviation) and 'l' is found in the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
'a' could be 'an' and 'an' is found within the answer.
'guys' could be 'men' and 'men' is found within the leftover letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for melanin that I've seen before include "Light-absorbing skin pigment" , "tanning agent" , "Pigment that accounts for skin colour" , "Brown skin pigment" , "Tanning pigment in skin" .)