Your thread, your rules. But the word “multiple” has no such restriction: Multiple" means "more than one," not “more than 2.”
Ink is not a colorless thing (ignoring invisible ink, here).
Google on “green magic” and you’ll get lots of hits, so I suppose that could be added to that spectrum. Probably other colors, but I’m not going to waste time googling them. If you look through enough fantasy stories, you can find many different magic colors, including octarine.
It seems to me that there are things that have “single”, “dual”, and “multiple” or 1, 2, and multiple as options or categories. Can’t remember any off-hand though.
Some states still have blue laws. Some comedians still work blue.
Black ice is not actually black.
Yellow journalism
The three movies in Krzysztof Kieślowski’s Trois couleurs trilogy.
Andrew Lang’s Fairy Books
The Blue Fairy Book
The Red Fairy Book
The Green Fairy Book
and nine other colors
also
The Blue Poetry Book
The Red Book of Animal Stories
The Red True Story Book
and a few others.
According to Herman Melville in Moby Dick, white is both of those things; it’s “the visible absence of color, and at the same time the concrete of all colors.” 
And, in legalistic and regulatory contexts, laws and rules often include an explicit provision that “words in the plural are inclusive of the singular and conversely” or words to that effect. Thus, the idea is that “multiple” can even include the “just one” case. But probably more than zero anyway.
I remember those too; I can still recall some of the nonfiction things I read (there was an article on “highway hypnosis” that really stuck with me). IIRC, the highest level was purple, which I thought was cool because purple was my favorite color at the time.
ETA: I found that the SRA Reading Laboratory is still available, although the color scheme is a bit more elaborate than what I remembered.
And, in fact, many languages have a grammatical “dual plural” form for things that come in pairs, distinct from the more general plural form. Modern English does not, but we have the idiomatic phrase “a pair of ______” to express the same idea.
White and black are each colors.
Just check out a box of 64 Crayola crayons!
~VOW
Additional SRA info: when our school was flooded with the SRA boxes, I discovered that classrooms of the same grade had different boxes. Playground bragging uncovered colors of different ranges. I was telling others I had reached silver, someone from another class said pink was their highest color.
It is not. However, when a corporation is bleeding red ink, or a newspaper receives a letter from the green ink brigade, one is talking about metaphorical ink, not the coloured liquid. (Though those expressions do seem to invoke the sometime use of the actual colours.)
So many colored alerts!
Star Trek fans will surely recognize a Red Alert, and the less common Yellow Alert. There’s also a more contemporary military alert scheme of Yellow, Blue, and Red Alerts in rising levels of seriousness and response, followed by White Alert, or all-clear.
In California, at least, the highway patrol (CHP) will invoke Amber* Alerts for abductions, and Silver Alerts for missing elderly. They also have the far less common Blue Alert where the public’s help is requested to find someone who has assaulted or killed a law enforcement officer, and the Yellow Alert, which has something to do with finding hit-and-run perpetrators. The Blue and Yellow Alerts may be purely internal to the CHP as I’ve never heard of them in all the time I’ve lived in California.
Other states are introducing Green Alerts for missing at-risk veterans, and Purple Alerts for missing adults with mental/developmental disabilities. Texas has a version of Purple Alert that they call a CLEAR (Coordinated Law Enforcement Adult Rescue) Alert.
- Originally, Amber Alerts were named for Amber Hagerman, who was abducted and murdered back in 1996, There is now a rather tortured backronym to fit into her name: America’s Missing: Broadcast Emergency Response Alert, or AMBER Alert.
And the four hijackers in The Taking of Pelham One Two Three:
There’s several collars related to employees:
White collar - management and professional
Blue collar - production labor and skilled trades
Pink collar - stereotypical female jobs
Maybe 
others
from Wikipedia:
The 16th century chronicler Alexander Guagnini’s book Sarmatiae Europeae descriptio wrote that Rus’ was divided in three parts. The first part, under the rule of the Muscovite Grand Duke, was called White Russia. The second one, under the rule of Polish king, was called Black Russia. And the rest was Red Ruthenia.
Matt Groening did a bit about this, something like “The Gold Group will meet in this room, the Silver Group will meet across the hall, and the Brown Group will meet in the basement.”
I was today years old when I first heard this expression. I’m not sure why I never heard it before - coined in the 1970s, and Google gives no indication that its use has declined since then.
There was a news story some years ago about Girl Scout leaders skimming the proceeds of cookie sales…which one columnist waggishly described as “green-collar crime.”