Aren't colorfast (5)
I believe the answer is:
bleed
'aren't colorfast' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bleed that I've seen before include "Lose blood" , "Squeeze money out of" , "Haemorrhage" , "Lose life-sustaining fluid" , "What would ancient doctor do" .)