The following link provides useful guidance on graph accessibility: AccessibilityOz, HTML5, forms, ARIA and JavaScript features(Opens in a new tab/window).
You can test your graphs using one of the many free tools that are available online for checking colour contrast and the effects of colour impairment, such as:
Stark(Opens in a new tab/window) – contrast checker, colour checker and colourblindness simulator
Contrast Checker(Opens in a new tab/window) – colour checker and resources
ColorBrewer(Opens in a new tab/window) – suitable colour palettes based on the requirements of your plot
Color Safe(Opens in a new tab/window) – aimed more for designers
Color Tool(Opens in a new tab/window) – for checking contrast and colour palettes at the same time
WebAim Contrast Checker(Opens in a new tab/window) – for checking size and contrast of coloured text
Color Oracle(Opens in a new tab/window) – colourblindness simulator.