The reason he's pink

It's very simple actually. At the beginning of development of Kirby's Dream Land, the first game on the series made for the original Game Boy handheld console and game which was released on April 27, 1992, there was a dispute over Kirby's colors. A famous developer Shigeru Miyamoto, better known for the Mario series, thought that Kirby should be yellow. On the other end, Kirby's creator Masahiro Sakurai, was certain that he wanted his character to be pink and not yellow. This dispute outlived the whole process of the first game, which resulted in official art to include Kirby in a white, monochromatic color scheme.

Regardless, once the second game came to be, it is revealed and established that Kirby is pink. A theory of why this was decided is that yellow would be too close a color scheme to fellow popular series, Pokemon. In Pokemon one of the most famous creatures is Pikachu, a yellow rodent like pokemon. Besides that, the only clear reason we have for Kirby being pink is simply that it was just the way the creator wanted it to be! Since then, Kirby has developed many more traits under his name and has conquered the hearts of nintendo fans all over the world.