The palette
The ground is a grey-beige weave with no accents, and against it the bayous should read as thin frank green: that is the master contrast of this map. Put your strongest colour in the motorway ring and the radial spokes, in clean lines rather than a wash. And give the water three different treatments rather than one, because it is three different things here: dark and winding in the bayous, geometric and pale in the ship channel, striped in the flood reservoirs to the west.