What we observe here in the sphere of physical light-activity is exactly what the light-ether performs on a higher level of nature when with its help the spiritual archetype of a plant takes on spatial appearance. For to this end the archetype, itself without spatial limitations, imprints its image into the tiny seed, whence the growing plant organism carries it again into space.
Then at once in the dark field of vision the positive facsimile of the window appears, woven by the activity of the blood which reproduces the outer reality. Having traced the colourless after-image to 'higher sources' that is, to the action of the blood let us now examine coloured afterimages. We need first to become conscious of the colour-creating light-activity which resides in the blood.