In 1995, the state adopted an official state tartan.
The colors are listed with the number of threads used to create the tartan. The sett for the New Hampshire Tartan is as follows:
green 56, black 2, green 2, black 12, white 2, black 12,
purple 2, black 2, purple 8, red 6, purple 28
The colors in the sett all have significance to the state. The purple represents the State’s bird and flower, the purple finch and purple lilac; green represents the green of the forests; black represents our granite mountains; white represents the snow; and red represents all the state heroes.
Source: New Hampshire Revised Statutes Annotated (RSA) 3:21
In 1993, the idea of creating a New Hampshire Tartan for the 20th Anniversary of the New Hampshire Highland games in 1995, was initiated. Designed by handweaver, Ralf Hartwell of Newton, NH, the New Hampshire Tartan is unique in its color tones, in that special dye lots must be prepared for the coloring process.
With the review and verification of the design as original and authentic by the Tartan Educational and Cultural Association and the International Association of Tartan Studies, NH State Representative Stephen Avery arranged for Governor Stephen Merrill to proclaim the Tartan as the State Tartan of New Hampshire in June of 1994. In January of 1995, Avery introduced a bill to the NH Legislature for permanent recognition, which was passed in May, 1995.
Source: The New Hampshire Tartan 
The New Hampshire Almanac is compiled by the New Hampshire State Library from state statutes and other sources as noted.
NH.gov - The Official Web Portal of the State of New Hampshire