coloring a area on map

Hi All,
Is there anyway to generate a separate layer with different color coding on areas based on some constraints.
For example, taking UK map I would like to have green color transparent layer on top of map for some areas in London. How do I generate the layer offline? Any info or articles already available will be really helpful.


when I go to and do a search for “layer”, there ate already some topics that come nera your aim.

For example:

You should also have a look at the OSM wiki … there is an app called TileMill …