The tests showed that the birds could see every nonspectral color that the researchers threw at them. Color pairs that were closer together in hue resulted in more mistaken visits but still beat the 50/50 odds of the control experiments. Even if the neural mechanisms for color vision were clear, and even if color-mixing experiments attest to avian tetrachromacy, we still could not answer the more philosophical question of what nonspectral colors really look like to birds. Does UV+green appear to birds as a mix of those colors (analogous to a double-stop chord played by a violinist) or as a sublime new color (analogous to a completely new tone unlike its components)? We cannot say.

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