It's sometime around the year 1030 in Cologne, Germany when Saint Bruno (well, just "Bruno" at this point in the story) is born. He grows up to be a pretty cool guy, teaching at the university and eventually becoming a celebrated dean and chancellor. But alas; Bruno just didn't feel satisfied with life. He didn't want to become a bishop, and he wanted more time for silence and solitude. He wanted to retire so he could follow his true calling: becoming a monk.
In 1084, Bruno and a couple of like-minded friends went off into the French Alps near Grenoble and eventually came upon a suitably remote spot in the Chartreuse Mountains. They established the Carthusian Order, which basically became the foundation of how a monk or nun should live; when you think of a classic monk and their life of devoted prayer and silent contemplation, Bruno and his friends started it. Bruno would eventually die in 1101, but before then he would establish another hermitage and be called to Rome to be by the side of Pope Urban II — a former student who would be remembered as the the Pope who started the First Crusade. The Order grew as time went on, gathering more people who wished to devote themselves to prayer. Five hundred years later, the Carthusian Order would receive a complicated recipe that claimed to be the "elixir of long life".
Chartreuse is a liqueur made from over 130 different herbs that need to be infused and macerated and blended together. The Order received the recipe in 1605 as a gift from one of the the King's marshals, but it took a century for them to study the manuscript and uncover how to make the complex elixir. Initially, they sold the 69% alcohol beverage as a medicine, but soon discovered that people were enjoying the naturally green liquid more often as a drink. They developed a milder version (only 55% alcohol) in 1764 that they called "Green Chartreuse," after Bruno's original hermitage in the Chartreuse Mountains (now the headquarters for the Carthusian Order), and in 1838 they produced an even milder "Yellow Chartreuse". About fifty years later, 'Chartreuse' started being used to refer to colour. It's difficult to ascertain if 'chartreuse' meant a colour that was similar to Green Chartreuse liqueur (a light apple-green, midway between green and yellow) or Yellow Chartreuse liqueur (a yellow with a smidgen of green).
Many people think of Chartreuse as more of a yellowish-green thanks to a computing RGB colour system in the '80s that went on to influence the web colours system we use today. In these systems, Chartreuse is the colour midway between green and yellow (in RGB terms, that's 50% red, 100% green, and 0% blue). In my head, I still think of it being more yellow.
Nonetheless, the liqueur name came before the colour name, not the other way around.
Thanks to Kelsey for suggesting this colour. If you're at all curious, check out Chartreuse's website for some more good times, or check out Robert Ridgway's 1912 book Color Standards and Color Nomenclature to see a colour sample of Chartreuse yellow on plate XXXI. Or, you know, you could just have some chartreuse, if you're into that kind of thing. Or not. No pressure.