What natural ingredients can be used to color food blue or green? I've been experimenting more and more with "natural" food colorings - meaning spices and other ingredients that naturally impart color as opposed to a commercial food dye made specifically for this purpose.

For example, I've let scallops (among other things) sit in a beet puree, and they get a brilliant pink color.  I plan on trying turmeric and saffron for more yellow/orange/red colors.

Are there other ingredients that I can try that might create a green or blue color in scallops? And would these work for other foods as well?
According to this blog, you can make blue dye from red cabbage, water, and baking soda. I don't know if it would specifically work on scallops, but I haven't been able to find any proof that alkaline dyes are detrimental to them. The article points out that they work for pastries, though. 

Spinach or matcha (green tea powder) could work for green dye. Matcha is already used, primarily in Japan, to dye several kinds of foods and/or drinks and I've personally used spinach to dye Easter eggs.