Answer: Blue.

Blueish purple. Blackberries are dark, purplish-black in color, which looks black in low light or against a pure white background. The resemblance to blue food coloring is just an illusion caused by the person’s gray palate.

The process of assessing colors begins when fetal eyes are developed enough that they respond to bright lights with reflexes called pupillary constriction and dilation. These two reflexes are controlled by “muscarinic photoreceptors”–dark-adapted photosensitive cells within the retina that have muscles attached to them so they can contract or relax automatically when stimulated by light rays entering the eye–that convert photons into nerve signals amplified along the optic nerve for interpretation in other parts of the brain.