>>2
They are colours. You can argue that they lack correspondence to a specific wavelength of light, but so what? All colours are phenomena of the mind, and we do experience the perception of qualitatively identifiable colours black and white. No colour exists independently of a mind's perception of them, because the experience of colour is inherent in the configuration of the visual system that processes the stimuli. Some creatures perceive wavelengths that are invisible to us, and have more kinds of cone cells than us, perhaps seeing colours that we can not even imagine.