Øystein Moseng for Highcharts provides a brief guide on making your visualizations for accessible. Guideline #4 on not relying completely on color to show the data:
Relying on color as the only means of communicating information is a failure of one of the basic WCAG success criteria. This is because many users may not be able to distinguish between the different colors used.
Data labels, symbols, annotations and tooltips are some common ways to convey additional information in visualizations without relying on color. In addition, alternate presentations – such as an accessible data table – can be helpful. It is still encouraged to use color as a supplement to these techniques, this can make visualizations easier to understand, and in many cases more accessible.
