It was fun using various foods to color my Easter cookies naturally this year. I chose a macaroon cookie made with egg whites. The colors were overall successful, but I think the liquid did cause the cookies to flatten some (although there were some other factors).
I tried a variety of natural colors. I tried collecting juice from frozen berries that were thawed, but since I was using small amounts that didn't always work. I did use a strainer for some, but then you get some pulp and that may not work for some things. The best way is probably to use cheese cloth, if possible, to just get the juice.
Turmeric - Mine was old but still had a smell. It didn't seem to affect the cookies right away, but I thought I detected a difference after a few days. Turmeric made a very nice bright yellow.
Blueberry - This made a bluish purple. I ended up using a strainer for this one. I did not try blueberries and blackberries together (supposed to make raspberry purple).
Carrots - Although shredded carrots seem to have the potential to stain my counter top orange, they did not produce enough juice to attempt to color my cookies. That idea will need more work since I do not have a juicer.
Blackberries - This was my favorite color which I would describe as a violet, or a soft purple.
Strawberries - I did get my pink after cutting out the white inside of the thawed berry and using the berry after straining.
It was fun and easy to experiment with natural colors from food.