Is there any posebility to change the current map colors to a darker color type ?
Unfortunately it's currently not supported change the map colors.
However this is a good suggestion and we'll investigate if this feature can be added in the future.
It is just a matter of your Map Framework.
U Can define every Map Framework you like under
WebOSMaps1.MapOptions.TileServerURL on Default there is a openstreetmap Server. But there are a lot of third party distributors that over other Maps than the default.
Please note that the TileServerURL functionality is only available in TWebOSMaps but not in TWebGMaps.
This is a limitation of the Google Maps API.