By stimulating certain cones with extreme precision, scientists can help humans perceive a new color that defies all comparisons.

"It is not a new color," John Barbur, a professor of optics and visual science at City St George's, University of London, told the Guardian. "It's a more saturated green that can only be produced in a subject with normal red-green chromatic mechanism when the only input comes from M cones." Barbur said that the work had "limited value."