Goal (level AA): Text (and images of text) have a contrast ration of at least 4.5:1, except where the text is pure decoration. Large scale test (at least 18 point or 14 point bold) or images of text can have a contrast ratio of 3:1.
The Colour Contrast Analyser (note the Aussie spelling) is a very capable tool for assessing color choices
Contrast between text color and its background; the smaller the text, the greater should be the contrast
Color choices that may not be very discernable by people with color blindness
Developing an understanding of the relationship between design ideas and visibility for people with various kinds of visual limitations
Use the Toolbar to evaluate the use of headings in the page, the presence and use of ARIA roles, the sequence of text in the page, and the division structure of the page.
The Toolbar has a whole set of tools you can use to figure out what is going on on a webpage
Use "Information -> View Document Outline" to see the structure of headings in the page. Are there appropriate headings and subheadings and are they hierarchical?
Use "Outline -> Headings" to draw outlines around headings on the page. Are all headings on the page outlined? Headings that are not outlined have been created without using the <h> tags and will not be interpreted as headings by assistive software.
Use "Information -> Display ARIA roles" to see how ARIA attributes have been used on the pages. Are there any ARIA attributes? If so, have they been used to identify the role of each of the major segments of the page?
Use "CSS -> Disable All Styles" to see what the page content is like without the color, font and layout provided by CSS. Is the text in a coherent sequence?
Free Voice Browsers
Apple VoiceOver screen browser is on every Apple desktop, laptop, tablet, and smartphone. Learn it. Use it to experience listening to and navigating your pages by feel alone.