Okay so look at the starting roster in Smash 64. These were the 8 most important Nintendo characters at that time. Now note the colours. Mario is red, Pikachu is yellow, Kirby is pink, Samus looks to be red here but her model is mostly orange, and Donkey Kong and Fox are both brown but Fox is a lighter brown and has a lot of white from his clothes. The only true overlaps are Yoshi and Link, who are both green.

Fun fact, in Ultimate, the starting roster is exactly the same. But look: Link is blue now. So now every starting character is a different colour. Coincidence? Yeah probably.