In Illinois we have the Illinois Information Technology Accessibility Act (IITAA) that applies to any organization that receives state funding. This includes public education institutions such as the University of Illinois. The law states:
Structure / Styling is Valuable
Most visual users can distinguish areas of a document such as what is a heading, where paragraphs break, list structures, and the flow of a document. Blind and those with visual difficulties who use assistive technology may not be able to do the same if a page is not structured correctly.
Don't use color only to convey information.
Charts and Pro/Con lists are a typical place where we see people use color alone to convey information. When these items are rendered in black and white, that information is lost. Just the same, when individuals who cannot see color, such as those who are colorblind, come across these pages they cannot understand the information.
The following are examples of line charts that use color to convey information. Although color can be used, using line styles as well is the best practice to ensure an accessible looking graphic.