There is blue corn, as well as most other colors as found in Indian corn. Supermarkets sell blue corn chips.

There are 'All Blue' and 'Yukon Gold' cultivars of potatoes. The 'All Blue' potato has blue to purple skin and blue to purple flesh and keeps some of its color when cooked.

There are 'Purple Passion' asparagus and purple string beans. However, they turn green when cooked.

Carrots come in white, purple, black, red, green and yellow in addition to the common orange.

A yellow-green cauliflower is available in addition to the usual white.

Onions come in red, yellow and white cultivars.

Sweet peppers come in yellow, orange, red, green and "chocolate" cultivars.

Eggplant comes in purple, black, white and green cultivars.

There are yellow cucumbers in addition to the usual green.

Anthocyanins are the pigments in many fruits and vegetables such as cherries, red cabbage, purple cabbage, red onions, grapes, blueberries, etc. Their color changes as pH changes so the color can be manipulated if you wish. The red pigment in most tomato fruits is lycopene, which is not an anthocyanin.

You could try the classic elementary school experiment on transpiration where water with food coloring goes up the xylem of celery stalks. The pale interior celery stalks work best.

You can blanch some vegetables to a pale yellow to white as done for white asparagus, endive or celery. You keep the plants in the dark by wrapping them with paper or covering them with a structure. You might be able to extend that technique to other vegetables by wrapping them with aluminum foil or other opaque material. With celery the leaf blades at the top are left uncovered. There are also self-blanching celery cultivars.

Visit seed company websites or get seed catalogs and you may find other different colors of common vegetables. Seed companies that sell via mail include Burpee, Park's, Thompson and Morgan, Stokes, Jung, Johnny's, Gurney and Henry Field. Especially check for "heirloom varieties", which may have novel coloration.

Color can be added to salads and other vegetable dishes with flower petals. Many flowers are edible including daylily, nasturtium, marigold, carnation, chrysanthemum and squash.

References

Re: Do blue potatoes get their color from iodine reacting with starch

Cabbage Juice - pH indicator

Re: What is in grape juice that stains your teeth so bad?

Re: Where do fruits and vegetables get their color?

The New Mighty Maroon Carrot

'All Blue' Potato Photo

White Asparagus

Edible Flowers thread in bionet.plants.education