gravitystorm/openstreetmap-carto — pull request #564 by floscher (2014-05-24 19:18:40+00:00)
Title: Made some line-colors dependent on their polygon-fill

I worked on resolving issue #57.

Objects with the following tags have now a border-color, that depends on the polygons fill-color:

* leisure
* swimming_pool
* playground
* track
* pitch
* tourism
* camp_site
* caravan_site
* picnic_site
* landuse
* field
* retail
* natural
* field
* power
* station
* generator
* sub_station
* substation
* amenity
* parking
* aeroway
* aerodrome

The dependency of both colors was expressed by adding:
```
line-color: saturate(darken(@color, x%), y%)
```
with 40 <= x <= 60
and 0 <= y <= 30

In my opinion this improves both the appearance and maintainability, because there is one variable per selector to define the colors of polygon-fill and line-color.

What do you think: Is this approach desirable for this mapstyle, or should the line-color rather be left hardcoded?