Quote Originally Posted by minimalistix
tartan.

Is there a major difference between what is used by Black watch and the Campbells clan regarding color.

Also why was the Campbell tartan adopted by the black watch?
Matt Newsome had a nice, concise post about this subject some months back:

Actually, the Black Watch tartan is the Campbell clan tartan. There is absolutely no difference in the sett whatsoever. Black Watch = Campbell. No difference.

In addition to being used as the Campbell clan tartan, the Black Watch is also used as a hunting tartan by Clan Grant and Clan Munro. And, because of its origins as a "government sett" it is used very often as a general use tartan by those with no clan connections.

It is not uncommon to find the same tartan shared by more than one clan, or having different names. For instance:
Campbell of Cawdor = Argyle District = MacCorquodale
Keith = Austin = Marshall
Hunter = Russel = Mitchell = Galbraith
MacIan = MacDonald of Glencoe
Morgan = Mackay Blue
MacDonald of Sleat = MacCullough

There are more, but this is what I can think of off the top of my head. What is interesting about the Black Watch, though, is not only that it is shared by three different clans (Campbell, Grant, and Munro), but that it is also a military tartan, and widely used as an all-purpose general tartan as well.
Note that the Grants and Munros also "claim" the Government Sett. All three clans were involved in the raising of the Highland Companies that formed the nucleus of the Royal Highland Regiment, or the "Black Watch".

Cheers,

Todd