Accessible tables do not use colour or shading alone to convey meaning. For example, the use of green, yellow and red squares to show low-, medium- and high-risk categories will not be picked up by a screen reader, and colourblind or vision-impaired users may not be able to differentiate the colours:

You can still use colours as an aid for people who are not visually impaired, but you should also include a text element that conveys the same meaning – for example, by writing values in the cells and providing a code below the table:

Better still is to write what the colour means in each coloured cell: