Can the color palette include any 4 colors?
If yes, what colors are gameboy-like?
If no, what colors?
Yes, the palette can be any 4 colours of your choosing.
The most typical gameboy-like palette is going to be one that looks like this: https://lospec.com/palette-list/nostalgia
But you can also use that website to find any 4 colour palette that takes your fancy (giving credit where needed), or make your own palette from scratch!
If you want to go for something other than the typical gameboy palette, as linked by taltuae, I would suggest the following:
https://lospec.com/palette-list/ayy4 (a very good palette by one of the hosts of this game jam)
https://lospec.com/palette-list/cosmic-cream-gb (good colour contrast, would likely be useful for a platformer)
https://lospec.com/palette-list/mist-gb (will provide a similar feel to the classic gameboy games if you're wanting a slightly different take on the typical palette while still maintaining the classic aethstetic)
https://lospec.com/palette-list/andrade-gameboy (a more desaturated version of the typical gameboy palette if you are going for a darker tone)
https://lospec.com/palette-list/coral-4 (this palette is useful if you need something more versatile and colourful for you vision of the game while still following the gameboy concept)
If you need anything more just set the filtering options to number of colours as 'exact' and set the limit to 4, there's plenty of good 4 colour palettes on the site.
https://lospec.com/palette-list
Of course, feel free to make your own from scratch or mix and match these palettes, the only limit is the number of colours.
I hope this can be of some help and good luck on the game jam :)
I don't believe that there was anything stopping the display of the Gameboy to be any colour, however they would likely have to be monochromatic. On a purely technical level I believe that the palettes that the hardware could display were purely monochromatic, with the proper Gameboy displaying a 4 colours green palette and specific variations having a 4 colours grey scale (this is from a very limited knowledge so feel free to correct me if I'm wrong), no idea the exact reason for this but is likely something to do with the technical capabilities. So, for a pallette that at least seems that the game boy could run, I would suggest that you could simply get a 4 colour monochromatic palette, such as the typical Gameboy palette, and hue shift it to the colour range you want. This will hopefully provide an authentic Gameboy feel. Another tip for keeping your colours Gameboy-like would be having a slight desaturation of the colours as I don't believe that the original game boy was able to display highly saturated colours. There's no right or wrong way of doing this and you can use any colours you want in order to complete this project.
Tldr:
While there wasn't any colour restriction on the hardware that I'm aware of, if you want your palette to be Gameboy-like you should pick one colour and make a monochromatic palette based off of that.
if you look through past jam entries (there are links to these on the jam page near the bottom) you’ll probably get an idea of what is allowed. i believe the original Game Boy could only display the same 4 colors (which appeared as shades of green) and no other colors. so if you want to be as authentic as possible, find a game boy palette (there are more than one because the exact shades of green are kind of debatable) like this one that Antigue Goose posted above. but any of the other palettes linked to above are also acceptable because the rules are any 4 colors, not just what the GB had.
as an example, for my past entries to this jam i’ve used palettes that use 4 different hues rather than them all being the same hue (green) like the original Game Boy. this is allowed, it’s just less authentic.
Snack Slugger,
Galactic Pizza,
Worm Life