From the Architects:
As an exercise in pure form, the houses were conceived together as two white monolithic volumes.
Together, they appear to be "floating"; a visually heavier volume juxtaposed with a lighter, more slender one underneath. This idea of contrasts is also applied to proportions throughout the elevations in a rhythm of voids and solids - openings and walls.
Inside, we also find this same idea of contrasts applied, although inversely - the "lighter" white volumes that make up the walls are contrasted with the visually "heavier" grey-coloured floors, seemingly grounding the entire composition.