Researchers at Univ of Rochester have discovered that Brilliant Blue G, a food dye, when injected IV can prevent secondary neuronal damages caused by an excess release of ATP into the spinal injury site.
The injection works only if it is done within 15 min after the injury and the skin turns blue for a while as a result.
The more interesting to us is the eyes now also appear blue (right). The pink hue of the paws, ears, nose, and the eyes (top left) is typical of the lack of pigmentation in this type of rats allowing the vascularity to show through.
Presumably then, a fair-skinned person, after consuming a large quantity of blue M&Ms, may develop dark blue eyes even if only briefly. The blue skin? We refer you to Star Trek (2009), Uhura's roomate (and Kirk's date) for more details.