The palette
The real contrast here is stone against grass, which is unusual in a city plan and worth leaning into. Warm, light values suit the ground: the magnesian limestone of the walls and the stone of the Minster ask for a cream rather than a white, and the Victorian brick of the suburbs takes a quiet russet. Give the strays and the flood meadows a frank green, greener than you would normally allow in a town, because their scale is the point. The Ouse crosses everything as one dark ribbon.