The palette
This is a city of stone and relief rather than water, so keep the ground quiet: the sandstone shifts from cold grey to honey depending on the light, which suits a greige field and a fine line. The one mass to commit to is Holyrood Park, and it wants a moorland green rather than a garden green, left rough so it argues with the two geometries in the centre. Treat the hollow between the towns as a pale band, almost a void: it is doing structural work, and filling it in would sew the two plans back together.