The ever-changing transparency of the Martian atmosphere makes it difficult to determine accurate surface colours from orbit. Scattering and reflection of light off atmospheric dust causes colour shifts between images, making a mosaic of many together show a colour patchwork effect. Up until now, suppressing this effect has had the consequence of diminishing colour variations over distances greater than the scale of a single image. Here, we made use of a new high-altitude observation campaign to construct a global colour model, which was then used to colour-reference each image of the mosaic, enabling long range colour variations to be maintained and revealing a much richer colour view of the planet than has been seen before.