Which common color usage mistake is illustrated in this chart?

A heat map is titled $?$Monthly Mean Daily Low Temperature for Indianapolis.? The heat map shows a $12-$by$-10$ grid with colored cells. The columns are labeled with the names of the months from January to December. The rows are labeled with years from $2010$ at the top to $2019$ at the bottom. The months of December, January, and February are in different shades of green, the months of March and November are in light shades of red and green, and the month from April through October are in different shades of red. The intensity of the redness increases from April through July and then decreases through October.

a$.$ Neglecting colorblindness

b$.$ Excessive color

c$.$ Unnecessary color

d$.$ Insufficient contrast