Using filled (choropleth maps) may be a little tricky. Every time you change the color range values you get a different map. That is why it is crucial to choose a proper method to define the legend ranges. You can find here three most common ways.
Filled map functionality of the Excel Map allows user not only to differentiate the shapes colors by values (which is sometimes called a choropleth map) but also to color them by categories. Using Excel Map France Postcodes (Code Postal) I will show you how to create your own regions.