Many thanks to everyone who replied. The suggestions offered have given me something to play with and think about.
One thing I have learnt is that designing for accessibility is somewhat a nightmare, certainly not an easy task. One would have thought by now that modern browsers would have some form of filters that could be applied to change colours for visually impaired users?
Whilst I don’t have the technical skills I do know any photo can be quickly visually changed by applying filter/s, so why not apply the same technology to a webpage?
Kind regards,