Yellow
Kirby loved all the colours of the rainbow, but one of his sure favourite colours was yellow, mainly because it showed up on a lot of things, like sunflowers, canaries, and...egg yolks.
Egg yolks? Some Smashers didn't really understand the logic behind it, but then again, yellow showed up on lots of foods, or as condiments for foods. Mustard, eggs, star-shaped cookies, fried rice, you name it; yellow really did show up on lots of those sorts of things.
Of course, that made things difficult for Pikachu and Pichu. The first day Kirby met them, he thought they were huge, walking egg yolks. The poor pink puffball got electric shocks from the both of them in response. He still mistakes them for that sort of food to this day, though only occasionally.
Kirby had even mistook Link's hair for egg bread once. The poor Hero of Twilight had to get all the rest of the male Smashers to pull Kirby off him and tell him that hair was not meant to be eaten, ever.
Really, the simplest things got Kirby into a load of trouble, especially if they were his favourite things.