World I'm building a sports league. The sports league has 21 teams.
This led me to a question that's an interesting intellectual puzzle I thought this forum would like:
Could the 21 teams wear different strips/kits/colours? They would have to be distinguishable at a glance.
Say you want 6 teams to have visually distinct kits, that's easy: you have a black, white, red, yellow, green, blue team. The more you have the harder it becomes.
(Obviously real teams just have an alternative kit they wear when there's a danger of confusion. I'm trying to avoid that because it makes them less strongly branded, weakens their sense of identity that little bit.)
Searching led me to this List of 20 Simple, Distinct Colors. Let me draw your attention to the 'Convenient' ordering at the top. ("I’ve arranged the “convenient” order so that if you want six colors, for example, just choose the first six. The order of the colors is inspired by their frequency of appearance on all the world’s subway maps (yes, I did count them all!)")
So you might say: "Well there you have it, 20 distinct colours, use those." But A) they're not quite distinct enough (the list includes green, lime, and mint), and B) that list was built with a constraint we don't have: we don't have to have one colour.
A team with a red strip like Arsenal is distinguishable from a team with red-and-black stripes like AC Milan, (IMO: maybe someone will argue). You don't have to use a new colour to create a new strip.
There's also shapes to think about. Imagine Team A has yellow-and-black vertical stripes, and Team B orange-and-black vertical stripes, that's a problem. But if we make one team's stripes horizontal instead of vertical, that helps a bit.
Contrasting colours might be useful here: a team in blue-and-yellow can play against either a team in blue or a team in yellow without a problem.