It would be useful to have an icon displayed that marks the threads that I have posted a comment in. So I can easily track conversations I was having and followup without having to subscribe.

This is a feature found on Brighthand forums.

The other thing is the color of the buttons under the Internet Tablet Talk logo at the top of the screen. The grey background and seemingly white text is not displaying properly. Actually I cannot see the words at all.

It's there already; depends on which theme you use, of course. In a pinch, though, you can use advanced search to find all threads with your posts in them.In Classic theme, at least, some of the colors are pretty whacked up that way. (Mouseovers, especially.) I use browser CSS to fix that.

So I have to change my browser settings in order to maximise my experience here?

I do not see themes anywhere on the site.

Go to "User CP", there are options for how the website looks when you are logged in. I don't think you have to use CSS to make the website to your liking.