I have build up manually a tile server on Ubuntu 14.04. LTS, by following switch2osm's guide and have used the openstreetmap-carto style.
Now I intend to add a base layer, underneath the current one, that will display the contour depth lines.
That's why I want to make the water transparent.
How can this be implemented?
I have seen in the scripts/ directory the generate_roads_colours.py. Should I create a new script for water in a similar manner, or one exists?