Besides adding colors to your map manually, you can also create a choropleth: a map which uses differences in color gradients to indicate the a range of values represented on the regions or states within your map.
This is also known as an area-value map. This can help you visualize your data based on the states or countries in the map spreadsheet. First, enter your data in the spreadsheet (example shown here is Population by State), then click Data Visualization.
Second, select your colors or gradients. You'll need to choose a start color, first. Then for the end colour to be a lighter or darker shade of the start color, select the same start colour and then click the "+" to open the color wheel, and select a position in the color wheel for a different shade.
When the Area Value Map setting is toggled ON, you will need to choose which data you want represented. Then, the colors will represent accurately the column of data in your map's spreadsheet.
Have fun making your maps fun and colorful!