Its name escapes me, there's a website which you enter a url, it goes and fetches the css, changes the colours such that I can't differentiate it from the original but a normal person would. By my wife'a account there are really huge differences between the two. I'll probably not be able to distinguish some colours where the green component makes the difference.

Here's one I've played around with.

http://colorfilter.wickline.org/

I'm not really clear on how it or color blindness in general works. So I don't know if finding the filter which makes the image unchanged for me (color-blind) is a good way of representing how the world looks to "normal" visioned people.

Thanks, that was it. No, it's not about representing how the world looks to normal visioned people, it's about how we cannot differentiate between some colours, or all colours for the worst case.

Deficiency doesn't mean that he sees colours diminished in hue value, but exactly that he wouldn't be able to distinguish between some colours.