Select an Appropriate Color Scheme in Charts

Consider the choropleth maps of average annual temperature by state shown in Figures $4\mathrm{.}1$ and $4\mathrm{.}2.$ We learned how to indicate the gradient of a quantitative variable, such as temperature, using different levels of luminance for the same hue, and how we can play on the psychology of color to convey coolness $($blue$)$ vs$.$ warmth $($brown$)$ in the audience. Suppose you need to create a choropleth map of median family income by state $($data not available.$)$ What color scheme would you choose to convey the message to the audience and why? Define the color scheme, hue, and luminance selected for this case.