Colour discrimination

This morning I opened the curtains to my balcony and saw that all the white coloured clips from my clothesline were lying on the floor. I picked them up and put them back on the clothesline. The other clips were not disturbed. I walked away confused. Then I heard a commotion in the balcony. I turned around and saw a crow trying to disengage a white coloured clip from the clothesline. Mystery solved!