Color-blindness occurs when a user is unable to see visual differences in charts and other graphics. Typically, a visual difference like a title background color displays a distinction between the title and the background. However, for a color-blind user, that visual difference is no longer noticeable.
A rule of thumb is to use a maximum number of six colors in data visualizations. Any more and it becomes very difficult for users to see the differences. It is also recommended to test screenshots of visualizations for color-blindness using online tools such as Color Brewer. These tools contain pre-selected and/or pre-tested color sets that you can leverage.