Here’s a tip to help you get your head around the idea of accessible website design: start with the assumption that you cannot predict the access needs of your audience.
For example, a person with Dyslexia may need a particular combination of text and background colours to comfortably read text on a web page. You could contact a person with this particular impairment and ask them about their preferred colours; but do all people with Dyslexia have the same access needs? Unfortunately – from a web designers point of view – the answer is no.
A better approach is to design pages so that the presentation of content can be changed by the end user; in the case of the above example, ensure that each person can change the colours to suit their own needs (e.g., via browser preferences or a style switcher).
This approach can be applied to all presentation aspects, whether it be, text size, layout, or the choice to leave graphics on or off.