The Will to Power · Friedrich Wilhelm Nietzsche
505.
Our perceptions, as we understand them--that is to say, the sum of all those perceptions the consciousness whereof was useful and essential to us and to the whole organic processes which preceded us: therefore they do not include all perceptions (for instance, not the electrical ones);--that is to say, we have _senses_ only for a definite selection of perceptions--such perceptions as concern us with a view to our self-preservation. _Consciousness extends so far only as it is useful._ There can be no doubt that all our sense-perceptions are entirely permeated by valuations (useful or harmful--consequently, pleasant or painful). Every particular colour; besides being a colour, expresses a value to us (although we seldom admit it, or do so only after it has affected us exclusively for a long time, as in the case of convicts in gaol or lunatics). Insects likewise react in different ways to different colours: some like this shade, the others that. Ants are a case in point.
Text from Project Gutenberg, public domain in the United States.