We must remember that on first looking through the prism Goethe had immediately recognized that the appearance of colour is always dependent on the existence of a boundary between light and darkness - in other words, that it is a border phenomenon. What colours appear on such a border depends on the position of light and darkness in relation to the base of the prism. If the lighter part is nearer to the base, then blue and violet tints are seen at the border, and with the reverse position tints of yellow and red (Plate B, Fig. i). Along this path of study Goethe found no reason for regarding the spectrum-phenomenon as complete only when both kinds of border-phenomena appear simultaneously (let alone when - as a result of the smallness of the aperture through which the light meets the prism - the two edges lie so close that a continuous band of colour arises). Hence we find Goethe - unlike Newton - treating the two ends of the spectrum as two separate phenomena.