Source for Median Household Income: here
How is the color coding established?
With the exception of the Median Income metric, I look at which city/zip has the highest and lowest cases/deaths and use that to calculate a range that is evenly divided into the 7 colors that I display above. This makes it so that the view is always automatically updated over time to compare citys/zips relatively. In some cases, I ignore clear outliers in the calculation of the range.