Short answers
Blue color is not only rare in edible organisms – Blue color is rare in both the animal and plant Kingdoms in general.http://biology.stackexchange.com/a/56478
and…
Blue light is the most available, most high-energy light that continues to reach plants, and therefore plants have no reason not to continue taking advantage of this abundant high energy light for photosynthesis.http://biology.stackexchange.com/a/56498