They went with pure B&W palette, but I'm surprised they didn't go with a nostalgia green palette (especially over that hideous B+Right palette).

@Geonjaha
Is that for all of the games? because I remember seeing a video of KDL where everything was actually the correct color (Kirby was pink, plants green, etc)
But that's also really cool! I actually might pay a small fee (maybe 50 cents) to make this available for all compatible GB games.

Pulls out the GBA SP and Kirby's Dream Land cart to check

Nope, possibly a custom palette. Kirby (and all sprites, since GB set a single "palette" for sprites) are pink, and it's winter in Dream Land (white ground, grayish-blue sky, and the other two colors for the BG layer are black and dark green).

(and it's debatable whether pink is the "correct" color for Kirby in the original game.
He was white on the cover art because (I think) Iwata and Miyamoto couldn't agree on his color. Iwata wanted pink and Shiggy wanted yellow. Well, he got his yellow Kirby as Player 2 in Kirby's Dream Course. ) )

Those are the palettes that are applicable to all games, but many Game Boy games came with custom palettes built in -
Eg. Mega Man games have Mega man as blue with enemies red, and Metroid II maintains some distinct colours.