Green buttons can be clicked (red buttons as well -- you will get them only in rare situations, though), the grey button is your currently active character.
If you have the "Builder class character", then you probably have Bob's Character Classes active. That mod provides alternative characters -- but it doesn't change their graphics, it's about other differences. Hint: Open your crafting menu (<CTRL>+<E>) and count the available inventory slots, then change to another character and count slots again. :-)
You should be able to hide the window by pressing the button labeled "Appearance" above it. In version 0.0.14, the GUI would be closed if any character button had been clicked. Personally, I think it's quite a nuisance if I have to re-open dialogues again just because I dared to press a button. Therefore, I've made the new behavior (you've to press the "Appearance" button in order to toggle the list) as a feature. Basically, all that was involved was adding a condition test in just one line. It wouldn't be hard to add another setting to change the behavior. (Only I feel a bit bad about requesting yet another French translation of just one string.)
Hope this helps a bit. I'm not really an expert regarding GUI design. I made it in a way that I believed to be obvious and intuitive -- but I didn't have a chance to test it on other people before uploading ...