Matt--

Jack Daniel's Black Label is their "Old No. 7" Tennessee Sour Mash whiskey--the primary product of the Distillery--so nick-named because of it's white-lettering-on-black label. They also have a cheaper (price-wise) line with a green label. Some years back, the Distillery introduced a premium line called "Gentleman Jack", which also has a black label.

The Jack Daniel's Distillery web page.

David
Tennesse Squire