The various objects shown on a map with colors other than blue depends on the type of map in use. Green, for example, can stand for changes in elevation in physical maps, bits of data in choropleth maps or forested areas in road maps.
Brown is also a commonly used color across maps, with physical maps using brown for higher elevations above green and road maps using brown for deserts, national parks or reservations. Political maps often use the color black for cities and boundaries, while black is used on physical maps for roads. Red is another color used across multiple map types, with red representing the GOP party on many political maps, elevations below sea level on physical maps and highways on road maps.
The use of colors other than blue on maps does not equate the colors of the features represented. While blue generally stands for water, green for elevation could be used for grassy areas or stretches of desert. White, which is used for high elevations doesn't necessarily denote snow-colored areas either. With choropleth maps, which shows different statistical data for a region, the colors have absolutely nothing to do with physical aspects of an area, but are used only to report different levels of the data being shown.