Colour is both spatial and material. It is an integral feature of architecture, yet, it is often undervalued, particularly in contrast to form. This article explores how Eileen Gray’s background in fine art and material practice promoted a particular use of colour in her architecture. Art practitioners who engage with processes of colour and material making are alert to the ambiguous nature of colour and its potential to contribute to space production. However, such knowledge is often overlooked by historians or dismissed as less significant than other aspects of design. Previous architectural histories of Eileen Gray that rely upon representations of her work in black and white photographs have missed the spatial and place-making qualities of colour in her work. Archival evidence, by contrast, reveals the significance of Gray’s material and practice-led colour research, which resulted in her distinct approach to modern architecture.