Mast lights on English tugs if memory serves me correct,
Single masted tug
very top "all round" view = Anchor light = white
Top Mast "Fwd" view = Towing of lenght exceeding white
Center Mast "Fwd" view = steaming light / Towing white
Bottom Mast "Fwd" view = steaming light white
N U C (can have two sets or one set seen from all around) they are from top of mast down "red -- white -- red"
to the stern normally above the stern light (white) is an amber or orange towing light (these can only be seen from the rear of the tug)
I may have this next bit wrong (I am an engineer after all) the mast lights
the very bottom one comes on with the port and Starboard and white stern lights, then with a short tow the middle white would be on and then with a long tow the top white would be on as well this denotes the type of vessel and how long the tow line is being used.
N U C (not under command) are used to denote restricted maneuverability.
Also day shapes would be hoisted BALL -- DIAMOND -- BALL to show others in the area of the restricted maneuverability
R, hope I got it right.