For basic bass colors make sure you get blue and black in both colorants and glitters. You'll also want watermelon and green pumpkin as colorants. Base colors like red, yellow, blue, white and black along with a color wheel would work also. Get 2 or 4 oz in the colorants and glitters, no sense spending a bunch on pints or quarts yet since you don't know for sure if he will enjoy this hobby or not.
If he fishes for panfish, (bluegill, crappie etc,) look at panfish baits at someplace like Bass Pro Shops or Cabela's to determine the most popular colors of colorant and glitter.
Canga and Buckeye both have good lists.