When the white area between the dark ones is large enough, the result is two sets of border or edge colors; red and yellow above, blue and violet underneath. By narrowing the white area, the yellow from the upper edge colors and blue from the lower edge colors mix and they form green. The result is a continuous spectrum, observed by Newton.

In Goethe's opinion, to say that white sunlight is composed of all the colors of a spectrum is just as absurd as saying that darkness is composed of all the colors of a spectrum. And then Goethe ”makes spectral colors out of darkness” by looking through a prism at an image having a narrow black horizontal line between two white areas. The result is a negative spectrum, having complementary colors compared to a normal spectrum – cyan blue above, then aniline red, and yellow at bottom. Goethe's intention was not, of course, to produce colors from black alone, but merely to show that having a black line on a white background is a complementary case compared to having a white line on a black background, and the result seen through a prism is also a complementary spectrum.

Since a physicist readily admits that this aniline red, which is not seen in a normal continuous spectrum, is a mixture of the colors red and violet (or the mixture of wavelengths corresponding these colors), it is odd that it is not seen that the color green in a normal spectrum is a mixture of the colors blue and yellow (when speaking in terms of color). It is even more odd, since the color green is actually seen as a mixture of different wave lengths of electromagnetic radiation. Aniline red and green are complementary colors having a similar origin in the mixing of different prismatic edge colors.