Red edges in fleece (7)
I believe the answer is:
'red' is the definition.
(I know that red can be written as crimson)
'edges in fleece' is the wordplay.
'edges' becomes 'rims' (rim is a kind of edge).
'in' indicates putting letters inside.
'fleece' becomes 'con' (I've seen this in another clue).
'rims' put into 'con' is 'CRIMSON'.
(Other definitions for crimson that I've seen before include "Deep red colour" , "Microns of colour" , "Become red-faced" , "Vivid red" , "Looking embarrassed" .)