The only approved natural sources of blue coloring used in foods, so far, are grape color extract and grape skin extract. Both of these contain anthocyanin grape pigments
This paper describes the sources and benefits of natural blue colorings, with a goal of matching the artificial food dye color FD&C Blue No. 1.
The authors discuss the health effects of the most popular natural blue dyes used in food products, as can be summarized below in Table 5, and compares them to the synthetic dyes.
In addition to the above, the anthocyanins (found in berries, especially the skins) have been shown to help control diabetes and to prevent and treat neurological disorders. They apparently pose no threat to human health, being safe even at high doses.
Another blue color is Gardenia Blue (see “Genipin” in the chart above) from the forests of several Asian countries, where it has been used for about 30 years. It, too, appears to have a number of therapeutic effects — makes one wonder if this paper is actually about the safety of food dyes or the suggestion for their medical uses.
Another suggested (but apparently not currently used) source of blue dye is the genipap fruit, native to Brazil. It can scavenge free radicals and may be effective against breast cancer and glioma cells. Other sources of blue color are algae (cyanobacteria) and natural indigo.
The above natural dyes are compared to the synthetic Blue 1 and Blue 2 dyes. Blue 1, in particular, has been found to inhibit neurite growth, suggesting neurotoxicity. You can see more about that at Lau (2006)
QUOTE: “Studies on laboratory animals suggest that synthetic food dyes may also be possible triggers of ADHD, as well as of anorexia and other behavioral changes.”
As for Blue 2, the authors note it is not considered genotoxic, but they complain that the two mouse studies done on Blue 2 and cancer were shorter than two years.
NOTE: Since mice only live about two years, how to fix the above complaint is problematic.
The authors further note that Blue 2 seems to increase brain gliomas (tumors) and mammary gland tumors (breast cancer) in rats. They conclude:
“Given this increased incidence of tumors, especially
brain gliomas, in rats, Blue No. 2 cannot be considered safe
for human consumption.”