You can paint them any colour you want. If you want to have a more fluffy, lore accurate match you could paint them as one of the
Dark Angel successor chapters. Follow the links to them to get their colour schemes.
I'm going to be using my
DV Dark Angels as Blood Ravens, a red and bone scheme with black or gold detailing. Will require some modification of the chapter symbols but thankfully it doesn't look too hard to change the sword on wings to a blood drop on wings.