As far as snacks go, rainbow colored Goldfish by Pepperidge Farm are the perfect bright-colored snack to help teach your child purple, orange, red, yellow and blue. They are handy and portable and make very little mess.
Other brightly colored packaged foods include colored cereals such as Trix cereal by General Mills, or Froot Loops Cereal by Kellogg's. These fruit-flavor based cereals are brightly colored to imitate the appearance of fruit, and they come in colors ranging the full spectrum. They can be eaten dry, so you can allow the children to allow them to separate the pieces into distinct piles of color to help enforce the color differentiation.
Though not a healthy food, brightly colored cakes that require the use of food colorings and dyes are popular among young children. Rainbow-layered cakes decorated with colorful sprinkles will draw the attention of most young minds, allowing you to note the colors as they devour the layers.
As with cake, ice creams and candies should be saved for dessert, though their bright colors are an advantage (despite the sugar content) to teaching children about colors. Store-bought ice creams come in nearly all color shades; pink, brown, white and even orange, blue, red and green. The candies on top of the ice cream, however, are what give it one of its greatest appeals. Colored candies such as jelly beans, Skittles, M&M's, Sweet Tarts, gummy bears, and virtually all fruity flavored candies come in every color. Your child can learn and thoroughly enjoy simultaneously. Hold a piece of candy up and ask "what color is this?" When they get the color right, reward them with the treat.
On the opposite spectrum of cakes and candy are the healthy food options that can help teach your kids about colors. Salads are the best way to incorporate multiple colors into one dish. Fruits are bright and come in virtually every color of the rainbow; cut up apples and cherries for red, oranges or mango slices, bananas and pineapples for yellow, kiwis or green grapes, blueberries, pink watermelon and purple grapes or plums.
Continuing the healthy trend, vegetable salads can also incorporate multiple colors, though with more subtle shades than those of fruits. Green leaf lettuce or spinach paired with bright orange carrots or squash, red beets, yellow corn, black olives and eggplants (if adventurous) will allow your child to have a full spectrum of healthy and colorful vegetables at their fingertips.