Depends on the type of map you're looking at. Be more specific.
world map
Different colors on a map typically represent different categories or types of data. For example, in a topographic map, different colors may indicate varying elevations. In a thematic map, colors may represent different levels of a particular variable, such as population density or average temperature.
By adding a mod such as the Color Map Mod
the part of the special-purpose map tells what the colors on the map mean is the key. the reason is because on the "Special-Pourpose Map" because the type of key there is on the map is called "Climate Regions".
all the colors
represent
choloropleth
Map colors refer to the use of different colors on a map to represent different categories, themes, or data. For example, a map might use green to denote forests, blue for water bodies, and red for urban areas. Color coding helps make the information on a map visually clear and easy to interpret.
legend
colors
mountain ranges
so you can know what the colors on the map means