A guide to Super Smash Bros. Wii U/3DS's many alternate costumes

Olimar

Red: Could this be a reference to Olimar's similarities to Mario?
Green: And this one is meant to reference Luigi?
White: --
Alph: Just as he did in Pikmin 3, new protagonist Alph takes over the second half of Olimar's alt costumes.
Alph in Green: A tribute to Alph's Pikmin 3 costar Charlie.
Alph in Pink: Another Pikmin 3 tribute, this one to Brittany.
Alph in Red: --

Pac-Man

Blue: Every one of Pac-Man's costumes with winged boots is a reference to the Magic Boots power-up from Pac-Land.
Yellow: --
Black: --
Purple: --
White: --
Red: --
Polka Dots: --

Palutena

Pink: --
Yellow: --
Green: --
Blue: --
Hot Pink: This is a reference to her fellow goddess, the rather annoying Viridi.
Black: Her dressed as her nemesis from Kid Icarus, Medusa.
Purple/Pink: A tribute to Uprising's sassy archfiend, Hades.

Peach

Red: --
Yellow: This look is the closest you'll get to Daisy being playable in Smash Bros.
Blue: --
Green: A secret message of her love for Luigi? Nah...
White: --
White/Red: Her Fire Peach look from when she finally got to pick up the Fire Flower in Super Mario 3D World.
Black/Gold: --

Pikachu

Red Hat: Pikachu dons the hat of Red, the lead trainer in the first Pokemon game.
Green Bandana: The headband worn by the star of Pokemon Emerald.
Blue Goggles: Pichu wore these same goggles as an alt in Melee.
Backwards Yellow Hat: The headwear of the boy trainer in Pokemon Gold/Silver.
Party Hat: --
White Bandana: --
Red Cap With Sunglasses: The standard headgear for the male protagonist in Pokemon X and Y.

Pit

Yellow: --
Pink: --
Green: --
White: --
Black: The look that would inspire the creation of Dark Pit, who is now a separate character.
Light Blue: --
Pink: --

Rosalina

Pink: A reference to fellow royalty, Princess Peach?
Yellow: A tribute to Daisy?
Teal: --
Red: --
Purple: --
Black: --
White/Red: A reference to her Fire Rosalina transformation from Super Mario 3D World.

Sheik

Red: --
Blue: --
Purple: --
Green: --
Black: --
Gold: --
White: The only obvious reference of all Sheik's alts, this one looks like Tetra from Wind Waker.

Shulk

White: All of Shulk's alternate colors represent his Xenoblade costars. This one is for Fiora...
Black: This one is Dunban...
Orange: This is Reyn...
Blue: This is Sharla...
Pink: This is Melia...
Yellow: And this one is Riki.
Swimsuit: And this one is just so Shulk can show off his bangin' bod.

Sonic

Purple: --
Light Blue: --
White: A reference to Silver, space hedgehog?
Black: A basic recreation of Shadow the Hedgehog?
Yellow: --
Green: --
Orange Shoes: The brighter blue is meant to remind you of Sonic's original design?