OSM is a database and therefor it hasn’t any kind of style or color.

I assume you’re referring to the Map displayed on OSM.org . This map is generated by a program called Mapnik. There are other programs with different purpose using different stylesheets, eg. Osmarender (try a click on the blue plus-sign on the top-right corner).

So if you want to have data rendered in a certain manner you might find someone in the web already providing a map or you have to generate your own map (eg. with mapgen.pl)