After a bit of fiddling around I added the extension "Color Links" and it seems to work well. Thank you very much Chris

@leocg Thanks for your reply, it is appreciated. At least in Chrome there is an extension that can used. 10% of all males are colorblind. I find it incredible that such large companies don't provide this simple request. How do you ensure that you don't visit the same address in search?

I have just moved over to Opera from Chrome and so far very happy ... Except I can't see how to change color of visited sites? Surely this would be relatively standard? Chris