Consider this .

""The Black Watch - The Clan Grant Hunting Tartan
The "Black Watch" sett in the Ancient Colors is known as the Grant Hunting tartan. This is the Hunting Tartan recommended for Clan Grant by our Chief. "Hunting" tartans supposedly developed as alternate tartan setts for the clans, with darker colors, and worn while "hunting" because it acted as a better camouflage outdoors (the belief being that the standard or "dress" tartan setts, with brighter colors, would scare off their quary).

The Black Watch tartan is the Grant "Hunting" tartan due to our clan's long association with this regiment. The original Black Watch regiments enlisted men from Clan Grant, and it is said that this tartan was originally a Grant tartan before being adopted as the official tartan of the regiment. There are many clans, such as the Campbells, whose standard tartan is identical to the Grant hunting tartan, or other clans, who have a variation of the Black Watch tartan (typically with lighter colors, an extra stripe, or a light stripe somewhere in the sett, etc), whose clan members were part of the original Black Watch Regiment and adopted the Black Watch tartan or a variation of it as their own. The Black Watch tartan in the modern colors is currently one of the most recognized tartans in the world, and is one of a handful that are considered by many to be a "national" tartan for Scotland. ""

http://www.clangrant-us.org/tartans.htm