The installation Color Shadows consists of two beamers whose light beam falls onto a wall from diagonally left and right respectively. On the wall the light adds up to a brighter color. Now, one places an object into the two light beams in such a way that two shadows are generated. In the left shadow, the right beam is covered. Only the light of the left beamer is visible and is perceived as yellow. But in the right shadow the light of the right beamer appears and is perceived as blue. By checking the colours of the emitted lights, one notices that from the right side, blue light is indeed projected. But from the left side only white light is projected. Nevertheless on the left yellow is visible. One sees a colour that is physically not detectable. This contrast phenomenon is also known as colour shadows.
If now the light colour of the right projector is changed to green, the colour green appears in the right shadow as expected. In the left shadow, however, a fine magenta appears this time, although the left beam is still white. In both cases, the projected light is physically identical, but it appears as a different colour depending on the context.
This is related to the white balance. Here, the total proportions of the different colors are added together and from this, a mean is formed that the eye interprets as white. In our case, the eye sees a white that is additively mixed with blue. The result is a white with a blue portion. The eye interprets this brightest and most extensive area as white. Correspondingly, the grey in the shadow is interpreted as one colour. It is always the complementary hue. In our first case with bluish white, the grey is seen as yellow. In the second case we see the complementary color of green, i.e. magenta.