, dye , and pigment . The optics of blue Colour Frequency Wavelength violet 668–789 THz 380–450 nm blue 606–668 THz 450–495 nm green 526–606 THz 495–570 nm yellow 508–526 THz 570–590 nm orange 484–508 THz 590–620 nm red 400–484 THz 620–750 nm Your eyes see blue when you look at light which has a wavelength between 450-495 nanometres (A nanometre is one-billionth