Hey Hubert. Yes, there is currently one theme available to address feedback from some users who wish to have a less colorful user interface.
We intend to open up theme designing to all our users soon, so do look out for that in the coming weeks. Once this is out you will be able to replace the colors of most of the UI elements, while some users with a knack for design can take this further by replacing some of the icons with custom-made ones as well.
So do look out for these upcoming changes coming soon.