At first glance, there is nothing self-evident or obvious about the connection between the colour grey and any particular kind of intellectual activity. And yet, upon closer inspection, our engagement with grey – which is often considered a non-colour that figures as a gradation between black and white, a shade on the achromatic scale – is intimately intertwined with philosophical thought itself. Unlike colours whose distinctness and intensity may distinguish them rather clearly from other pigmentations, grey lives predominantly in a world of shades. Located somewhere on the spectrum between the poles of black and white, what is called grey draws attention, each time it is perceived, to its own differential gradation, a gradation that sets each grey apart from other instances of greyness by merely a hue, more accessible perhaps to the eye than to the word. Like the experience of philosophical thinking itself, our encounter with grey thus pulls us into a world of nuances, subtlety and the exacting experience of fine differentiations. We may speak, for instance, of a warm grey or a cool grey, a light grey or a dark grey, an ashen grey or an anthracite grey. As the German art historians Magdalena Bushart and Gregor Wedekind point out, it behooves us to regard grey ‘not as a negation and a non-color’ but rather ‘dialectically, as a quality that consists in being nothing and yet something, an absence and a fullness, dead petrification and living bravura, a mode and a form of being’. This intricate form of being manifests itself in a plurality of perspectives. In the context of older art, we may be drawn to modes of philosophical reflection that are opened up by the complex grisaille technique in medieval panel painting and in Baroque oil painting, or by the subtly grey-suffused portraiture that we associate with masters such as Rembrandt. From among the most well-known paintings of the modern Western canon, we may be especially hospitable to the modes of conceptual enquiry instigated by the grey tonalities of Picasso's Guernica. Even though Picasso experienced a so-called Blue Period and a Rose Period, but no Grey Period, it can be said with confidence that, without his seminal engagements with grey, our concept of modern painting would be radically different – and impoverished.