example dungeon overlay for rendermode-options

settings.py

rendermode = ['lighting', 'dungeon']

custom_rendermodes = {
    'dungeon' : {
        'parent' : 'mineral',
        'description' : 'an overlay showing the location of dungeons',
        'options' : {
            'minerals' : [
                (52, (0, 0, 255)),
                (48, (0, 255, 0)),
            ]
        }
    }
}