Map Symbols
Orienteering maps are drawn using an internationally agreed set of symbols and colours to represent various features and there should be a legend printed down one side to explain the symbols used on that particular map (depending on the features in that area).
The following two links provide a complete list of map symbols used for normal foot orienteeing and for school orienteering.
Information provided courtesy of maprunner
In summary then
BLUE = wet stuff; ponds, streams, marshes, springs
BROWN = contour lines, pits, depressions (small hollows), gullies, knolls (small hills); "soft" manmade features like earth walls/embankments
BLACK = rock features such as cliffs, crags and boulders; tracks/paths; manmade features like buildings, footbridges, fences, power lines
WHITE = generally good news - open woodland with tall, well spaced trees making it easy to run through although there may be ferns or brashings on the ground
YELLOW = grassy spaces; a paler yellow for rougher terrain such as heather
GREEN = generally bad news - thicker woodland, difficult to get through and the severity depends on the shade of green - the darker it is, the more you really don't want to go there!