The jam page says, “The main condition is to create a game that uses any two colors.”

“Basic requirements for the game: the graphics should preferably be black and white,” which together means the closer the two chosen colors are to pure black (#000) and white (#fff), the higher the game should score in… the Art category, I’m guessing?

“Is switching between pallets allowed? (YES)”

Or wait, is that palettes can be each two colors that default to white and black?

Does this mean the graphics should be monochrome black and white while text and browser-based text decoration can be any two colors?

I saw someone mention previous jams like this that can be used for comparison on what dithering is allowed, if any, but there weren’t links to those jams or names to search on.

What exactly is allowed with color themes?

Edited to add a find: https://itch.io/jams/hosted-by-mylinemedia. Putting together previous jam guidelines might define them for this time.

The winner of the 6th edition is a game using dark blue/grey and grey, and the 2nd place in the 7th edition is game using 2 (or even 3 it seems, but maybe it is the compression of the images) shades of grey with dithering.

I think the black & white is a suggestion, as it is worded "preferably", meaning you can use any two colours but it is better to use black & white if you don't have any big art ideas, as it will have a better result than a weird pallet. It shouldn't have any impact on the score except if you use 2 colors with a weird contrast being awful for the eye (let's say pure blue and bright yellow for example).

Anything that in on the screen should stick to these 2 colors, meaning that you can't cheat by putting text in the HTML code outside of your game canvas, it will still be considered part of the game.

The pallet switching means that you can switch to any other 2 colours during the gameplay, as long as it is still only 2 colors. It can be useful to convey different moods if your game have multiple levels, as you can use different combinations of 2 colors per level.