I think most blue hues that occur in plants (food) are typically going to be more towards a mix of both colors. So stuff like blueberries and blue corn might counted as blue AND purple.
After a minute internet-search, blue pea flower (brewed to make blue tea), starflowers and blue spirulina (algae superfood) might be more common definitely-blue plants that people can eat.
There's also a lingcod (fish) that can have blue flesh rather than the typical white or pink. You "might" be able eat raw, but it more rare and you probably should cook it to the color white anyways.