Have you ever wondered why old photographs were only black and white? You might think that this is because people hadn't figured out how to make cameras use color. This is true, but there is a better reason: color hadn't been invented yet.
One day, in the country of Súiacuil, Colo Brun noticed that it was hard to tell things apart. There were outlines and shapes, but there was just one color, which they called L̊aight (pronounced sort of like "light" and sort of like "white").
He told this to Blæc Dærc, who decided that some things should not reflect light and named them after himself. He also decided that because people are sleeping anyways, there shouldn't be any light at night. Greigh noticed this and decided that there should be objects that are sort of Blæc and sort of L̊aight, and lots of shades of that color, and that they should be called Blæc Greigh, medium Greigh, and L̊aight Greigh.
Photography was invented shortly after that, and photographs used the new L̊aight, Greigh, and Blæc that had been invented. Colo, however, thought there should be more, so he invented Brun, and made dirt and wood Brun objects.
There was still something missing, though, so Colo asked people to invent new "colors." Blæc and Greigh came, of course, and also Redd, Arinj, Illo, Ŋreen, Blu, Wṛpḷ, Pŋ̣k, Sian, Mujent, Gold, and many others. Colo put six of the colors in order — Redd, Arinj, Illo, Ŋreen, Blu, Wṛpḷ — and called it a RAIŊBW. Other people got colors similar to the RAIŊBW colors — for example, Pŋ̣k got L̊aight Redd, and Indigl became a kind of Wṛpḷ (she tried to get into the RAIŊBW).
Each person who got a color then got to choose something to be that color. Blu, who was first, wanted everything to be his color, but Colo said that that wouldn't help anything, and they would be back where they started, so Blu decided just to have the background (now called sky) and water his color. Ŋreen went next and decided to make leaves her color.
Illo went next. She wanted leaves and sky, too, as well as everything else. She said that in the end, everything would be her color, and it became true. When the day ends, it is Illo. At the end of the year, leaves become Illo. When something burns down, the fire is Illo. Redd and Arinj also wanted that, so some of those things became Redd and Arinj.
Other things still had no color, so they were divided up so every color had something. They also decided that light should be bent, and that when it does, it should show the RAIŊBW. They also decided that colors should mix and how they should mix and that there should also be three primary colors.
Then color photography was invented.
I found another, much shorter version (I don't remember if it was an early draft, or if I just used the same idea twice), in which Color invents Red And Indigo: New Bender Of Waves.
He then threw the rainbow outside, and the world became colorful. The heavier colors—red and brown—hit the ground and the trunks of trees, and the blue was so light that it stayed in the sky above the clouds. The green, being in between brown and blue, ended up on leaves and grasses. Green and blue, however, weren't sticky, so they would often fall off - the blue fell off once each day.
Later, I translated this story into my conlang Lwaitel, and made some modifications; you can read the newer version. Differences: