Hmm, I've been using Chrometric to see how pages look for different types of colourblindness. It's open source so you could probably check out the filters they use.
> What you will definitely need is HTML/CSS/JavaScript, because you can't really choose languages in the front end (if you'd succeed writing everything with emscripten, I'd be very impressed)
Not really. Depends on what you want to do actually. There's a good framework called vaadin that does UI without any html or javascript. Pure Java and asynchronous. Huh... I actually miss using this framework... Weird.