His own observations led him to a definite experience of the quality of the colour blue, for which he coined the phrase 'feebleness of blue' ('Ohnmacht des Blau'). In some way this colour seemed to him to be related to black. In order to rouse his artist friends and to stimulate their reflexions, he liked to indulge in paradoxes, as when he asserted that blue was not a colour at all. He found, however, as time went on, that in this way he came no nearer his goal.