Any blanket is better than none, but IMHO wool is best. Naturally non flamable, warm if wet or damp, and does not attract or retain odours unlike synthetics.
I dont think that colour is important. Dark colors wont normaly be any warmer than light colours, the only exception being outdoors in cold but sunny conditions when dark colours would absorb a bit of radiant heat.
Orange or red are visable in most conditions, and dark colors show well against snow, but likely use is inside inside a vehicle or other shelter, not in the open.