The palette
The main contrast here is not land against sea but city against estuary, so give the water real weight: a grey-green holds the Mersey better than a frank blue, which would make it look like a lake. Treat the basins as dark, tight, regular hollows, because their rhythm is what the eye follows. The built fabric takes a brick tone, rust or brown, and the centre will have no other pause than its squares: a map cannot lighten a single district, so the St George’s plateau takes the tone of the city around it.