Pink has too much of a grey tint, as Dark Warrior said.
Peach blends in with Sonic's muzzle, and makes him and Knuckles look like that had there fur shaved off O_o.
Beige looks fine to me, I guess the brownish tint just turns off some people.
Purple is only 5 colors, but it still looks good.
White needs to appear as a lighter Silver.
Yellow is a little bright, but at least its a better "Yellow" then gold, which is fine, but too dull in color to be yellow.
Red, despite, it being the color I use, needs to have some light colors in it. The reason for having no "light spots" is because Red is 24 colors, and color changes are based on 16 colors. Instand of using the last 16 Red colors, SSN should "pick" colors in the red palette that look suit to have good shading.