While we prepare guidance, the web community have provided a wealth of knowledge and research on designing for a desired accessibility and usability.
As a minimum, each feature must meet Level AA of the Web Content Accessibility Guidelines (WCAG) 2.0.
Colours used on the Wiggle website must be compliant in contrast. A quick way to check contrast is to use a colour contrast checker.
You can use an automated tool to regularly test a features accessibility while it is being built and after it has been launched, for example on Wave.
The Government Digital Service in the UK have provided these handy guides to help designs build solutions with dyslexic, low-vision and for users on the autistic spectrum. They can be found on the Home Office Git Hub repository.
Test the website feature with users regularly with usability testing. This keeps the feedback loop going.
There are 285 million people in the world that have low-vision. Guidance on designing for screen readers can be found in the WebAIM website.