I'm not sure how Silv did it (I need to find out from him) but blocking the ability to post HTML is "by design". We don't really want people posting arbitrary images into the forums. It creates opportunities for people to plant malicious images and other code that needs to be moderated, and if not designed for, can destroy the layout of the forums.
As for forum colors, we also don't want you guys applying your own styles to the posts - at least, not in a way that's not provided by us. If we choose to change the theme later to something darker, for example, and you've set your own colors, it could render part of your text unreadable.
In the end, we want to give you all a minimum set of tools to style your posts so you can correctly convey your questions, answers, etc... but we don't really want to turn these forums into a vine or stream of lolcats (though I do love a good lolcat :P).
With that said, I appreciate peoples' desire to personalize and we're looking into adding support for profile pictures, etc... It may be we find a compromise somewhere, such as allowing you to post images within a certain size range, or posting images only directing to elsewhere on the website etc... Worst case, we can always grant the ability to post images within the Tavern, as that's really the place for those types of threads.