What does Eldunari look like?

In the Inheritance Cycle book series, Eldunari are described as being small, glowing orbs that range in color from white to blue to green to red. For example:

> Saphira gave one of her usual amused snorts. Eragon felt her amusement through their bond. She sounded delighted that he now knew something she could not tell him. Her Eldunari seemed to radiate a bright blue warmth.