It's not really a colour of the light, but only one of our brains. Red + Blue = Bran glitch? To get an idea of what this optical illusion is about in more detail, we have to see how our eyes work.

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency. An object appears to be black if it absorbs all the wavelengths of visible light. For example ...

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency. When white light passes through a coloured filter, all colours are absorbed except for the colour ...