Black is used as it does not rot like white cable does after it been in the sun after a while .I take it all the cables run in the same direction and it looks neatish .If they put a box in the garden or on the wall and everytime someone wants cable they run a cable from this box to the house each installer would run it a different way and it would look awfull seen this before .What we have done here a long time ago we used capping / trunking on the outside of the flats .This can be bought in differet colours .This is how we did the mdus in this area to keep the council happy