Graduate Color Fills and Classification Breaks
The use of Graduate Colors (a 'color ramp' or range of color values) is often used to depict an increase in some attribute of the data (e.g., population or rainfall). Note that these are not a proportional symbol (50% more red does not mean 50% more rain, it simply means more rain). Typically, darker shades of the color ramp indicate more of the attribute in question. Multi-color ramps (e.g., from green to yellow to red) can also be used, but these are less intuitive than a simple light-to-dark color ramp.
By default polygon layers (e.g., countries) are shown with Single Symbol (solid fill), with a random color.
Right-click on the layer in the Table of Contents and choose Properties to open the Layer Properties sheet
Click the Symbology tab. For graduated colors, click on Quantities and choose Graduated Colors
For the Field, use the drop down arrow by the Value box to choose a field (must be a numerical field)
The default classification uses 5 classes and Natural Breaks (in the data)
To customize the classification breaks you can change the number of Classes or click on Classify for more options
Choose a Method of classification
Choose a number of Classes for the method
Verify that the breaks (shown as blue lines in the graph) 'fit' with your data (shown as gray bars in the graph)...
Verify that the break values are what you want... (with the Manual method you can manually enter break values)
Choose a Color Ramp (typically a single color gradient)
The class Labels can be manually edited if you wish
Click OK or Apply to accept the settings
OPTIONAL: From the General tab, alter the Layer Name to better represent the symbology
Results: A graduated color ramp based on the specified number and method of classes, with a chosen color ramp
OPTIONAL: The name of the field being used for the classification can also be edited...
...or even deleted entirely
Final result with custom name