Dear Deborah,
In terms of the overall user interface, most of the MATLAB UI colors have been updated to meet WCAG AA criteria (see attached screen shot). Also, since R2022a MATLAB Online offers both a light and dark theme.
In terms of graphics colors, users can use the colororder function and specify the "dye" color palette. The colors on the "dye" palette meet international contrast ratio standards for enhanced accessibility against a white background. For example, specify the "dye" color palette for the plot. After plotting a graph, simply add the following line to the code: colororder("dye").
Thanks for using MATLAB Answers for your question and we hope this helps!