It's always been my understanding that the word "hunting" referred more to the earth-tones of the hunting tartans (green, brown, etc.) rather than the actual use of the tartan in the hunt.

The Scottish Tartans Museum's FAQ page has this to say about hunting tartans:

Hunting tartans came about in the mid 1800s when two versions of the MacLeod tartan were published in a book called Vestiarium Scoticum (later proved to be a fake--but there is not enough room to go into the history of this important book here). There was a bright yellow MacLeod (MacLeod of Lewis), called "dress" and a green and blue tartan (MacLeod of Harris) called "hunting." The green tartans became very popular after this and most families who had bright red or yellow based tartans designed alternate tartans with a green background (or sometimes brown) and called them "hunting." Families whose tartans are mostly green do not usually have alternate hunting tartans. These tartans actually had little to do with hunts.

-- http://www.scottishtartans.org/faq.html
I too have read statements about hunting tartans being used as camouflage on the hunt because of the muted tones of the colours, but I also remember reading another source that made the statement that this is a bit of a "roast chestnut", since some animals are colour-blind! :mrgreen:

So essentially, the hunting tartan is an alternative tartan for one in brighter colours.

Cheers,

Todd