Most American state flags are blue. So many, in fact, that flag scholars treat the "seal on a blue field" as a single genre with about two dozen members. New Jersey's flag escapes the genre by one decision: the field is buff, a pale yellowish tan that no other state uses. The color is not decorative. It is a direct reference to the uniforms of the New Jersey Continental Line, fixed by an order George Washington signed in 1779, and it makes New Jersey's flag one of the few whose background color carries the history rather than the emblem sitting on it.
Washington's buff and blue
On September 14, 1779, Washington ordered that the coats of the New Jersey Continental Line be dark blue with buff facings, the collars, cuffs, and lapels that showed a regiment's identity. This was a distinction. Buff facings had until then been reserved for Washington's own uniform and those of his generals and their aides. Blue and buff were the commander in chief's personal colors, and extending them to the New Jersey regiments set the state's soldiers apart from the rest of the Continental Army.
The following year the army's war office connected uniforms to flags, directing that each regiment's standards match the color of its uniform facings. For New Jersey's regiments, that meant buff. The nickname went back further still: the colony's troops had been called the "Jersey Blues" since the French and Indian War in the 1750s. When New Jersey needed a state flag more than a century later, the buff field was sitting in the historical record waiting to be used.
Du Simitiere's arms
The coat of arms on the flag is older than the flag itself by 119 years. In 1777, the state's new government turned to Pierre Eugene du Simitiere, a Swiss-born artist and collector living in Philadelphia who had become the young republic's unofficial designer of emblems. He served on the first committee for the Great Seal of the United States, and his work touched the seals of several states.
For New Jersey he drew a shield bearing three plows, an honest declaration of what the state's economy actually was. The crest above the shield is a horse's head over a forward-facing helmet; the horse, an old emblem of the state, was made the official state animal in 1977, and the helmet's forward position is read in heraldry as a mark of sovereignty. The supporters are two women. On the left is Liberty, carrying a staff topped with a Phrygian cap, the classical emblem of freedom that appears on a dozen American seals. On the right is Ceres, the Roman goddess of agriculture, holding a cornucopia. Below runs the motto "Liberty and Prosperity" and the date 1776, the year New Jersey adopted its first constitution. The arms were tidied into a standard official rendering in 1928, but the design is still recognizably du Simitiere's.
The 1896 flag
New Jersey went most of the nineteenth century without an official state flag, relying on militia colors and informal banners carrying the arms. The legislature formalized things in 1896, adopting the coat of arms on a buff field. Sources disagree on the exact day, with both March 26 and May 11 of that year appearing in the record, but the reasoning was documented in the General Assembly's minutes: buff was the color Washington had assigned to the state's Revolutionary regiments.
New York adopted a buff flag the same year, on the same logic, since Washington's 1779 orders had covered the New York line as well. The parallel did not last. New York's veterans and regiments had a long attachment to blue, and the state switched its field back in 1901, leaving New Jersey as the only buff flag in the union. It still is.
Pinning down the colors
For most of the flag's life, "buff" and "blue" meant whatever the flag maker had in stock, and renderings drifted from pale cream to deep orange-tan. In 1965 the legislature ended the drift. Chapter 170 of the laws of 1965 established buff and Jersey blue as the official state colors and defined them precisely, using the cable numbering system of the Color Association of the United States: Jersey blue is cable no. 70087 and buff is cable no. 65015. Few states have bothered to specify their colors to that degree, and it gives New Jersey's flag an unusually exact legal identity: a particular tan, carrying a particular blue, both traceable on paper to a general order written in 1779.
The flag flies over the State House in Trenton and on state buildings and courthouses across New Jersey. It has never been redesigned, and there is no serious movement to change it. Whatever its faults as graphic design, and a two-supporter heraldic achievement is not easy to draw from memory, the buff field does the one thing a flag most needs to do: nobody mistakes it for any other state's.
References
[1] "Coat of arms and flag of New Jersey," Wikipedia. https://en.wikipedia.org/wiki/Coat_of_arms_and_flag_of_New_Jersey
[2] State of New Jersey, "New Jersey State Symbols," NJ.gov. https://www.nj.gov/nj/about/symbols/
[3] New Jersey Revised Statutes, Title 52, Section 2-1 (state flag); Chapter 170, P.L. 1965 (official state colors).
[4] "Flag of New Jersey," Britannica. https://www.britannica.com/topic/flag-of-New-Jersey
[5] "New Jersey (U.S.)," Flags of the World. https://www.crwflags.com/fotw/flags/us-nj.html