This chapter closes Part II with a descent into Eliot’s post-Waste Land violet hour. His conception of the symbolic and spiritual function of twilight, light and darkness was informed by advances in the theorisation of colour at the emerging nexus of art and psychology in the work of (for example) William Wundt, and Eliot’s own psychologist Roger Vittoz. In Four Quartets the psychological action is accordingly located within a twilight space existing in the momentary psychic threshold between day and night. A disaffection with the ‘twittering world’ and an immersion in ‘the violet hour’ allows the poetic consciousness to perceive the dark substance of the shadows lying beneath the surface of reality. The dusk world is given muted colour, complicating and elevating it beyond shades of grey into the realm of aesthetics. The ‘dim light’ that transforms the familiar world into an uncertain psychic space is the sensory precursor to the aphotic deprivation of the poetic underworld briefly depicted in ‘East Coker’. When read in relation to a mixture of Einsteinian and Dantean images of light, this darkness becomes intelligible as the ‘Light Invisible’ of a spiritualised poetic universe.