Dropping yellow, German artist unfinished (6)
I believe the answer is:
Here is my best explanation:
'dropping' is the definition.
'yellow german artist unfinished' is the wordplay.
'yellow' becomes 'or' (heraldic term).
'german artist' becomes 'durer' (I've seen this before).
'unfinished' means to remove the last letter.
'durer' with its final letter taken away is 'dure'.
(Other definitions for ordure that I've seen before include "Excrement", "soil", "Dirt", "unclean", "Dung, filth" and "Filth".)