I would suggest dark brown, so any confusion with orange is pretty unlikely.
Red as line lets the hairs of any central european electrician stand straight up, because it was used as ground, and has been completely outlawed in the early 70ies. You can't buy red wire here, even if you want! If I ever get to Britain (before standardization catches) I'll sure enough return with at least 300m red 1.5 mm2 wire, just for nostalgia.
