how to look at the map in gray scale and overlaod KML tracks in color

on it to permit to discuss more easier on changes and new planings about circulation, new amenagements, bike way networks etc.?

There is not only one OSM map. Use an OSM-based map which is greyscale or make it greyscale in your own postprocessing.

You can use those premade map styles in your web/software application (whatever it is, you do not name it): see section “toner” on or . Always obey the copyrights and tile server usage restrictions, depending on your usecase.