LMMS is actually very themeable.
Here's a quick tutorial: http://lmms.sourceforge.net/wiki/index. ... ng_a_Theme
I hope we'll see one of your themes on the LMMS Sharing Platform someday
Good luck!
Make sure to search to see if your idea has been posted before! Check our issue tracker as well, just to make sure you are not posting a duplicate: https://github.com/LMMS/lmms/issues