Renzorex You can now add tag lines to your profile. I was working on adding it already :D Toxic is talking about adding an image to your profile, rather than the colour bar that is there at the moment.
Adding a custom banner is possible, but would need a large amount of work to implement. If there is a lot of demand for this feature, then I will work on it. If not, I don't think is really a needed feature personally, so won't bother.