David Wolfe has been really into the color of foods lately and will be releasing a book in the future called The Color Cure. Anyways, he says it's one of the most amazing discoveries he's made in his career (and that's saying a LOT!) and he found that the blue pigment, such as the phycocyanin in spirulina, is the best color. It's really rare too. So rare that plants usually fake it.
Blue-green algae, such as E3 Live, actually has twice the amount of the blue pigment though, but still spirulina is an excellent source of it and a fraction of the price.