WebAIM’s Contrast Checker can be used to check the color contrast of text against a background. According to the FHWA publication Creating Section 508 Conformant PDFs, text contrast must meet minimum WCAG (Web Content Accessibility Guidelines) 2.0 level AA requirements: a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text.
The National Transportation Knowledge Network (NTKN) hosts NTKN Communities of Practice: 508 Accessibility, a group of practitioners that meets periodically to discuss 508 accessibility and compliance. In addition to meeting minutes, Section 508 Helpful Links and Useful Tips is provided that, in turn, includes a link to Section 508 training and checklists for Word, PDFs, PowerPoint, Excel and Outlook hosted by the Social Security Administration.