Drop part of course on source of eye colour (4-5)

'colour' is the definition.
(sage green is a kind of colour)

'drop part of course on source of eye' is the wordplay.
I cannot really see how this works, but
'drop' could be 'sag' (sagging is a kind of dropping) and 'sag' is present in the answer.
'part' could be 're' (re is a kind of part) and 're' is found in the answer.
'course' could be 'n' and 'n' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?