First of all, great choice on the navy blue for the futon! It is such an understated yet always chic color. The key for futons is that they need pretty throw pillows to dress them up. I would say to add light toned throw pillows in color block patterns, and a throw blanket folded along the top back of the futon for added dimension (but also functionality in case you’re in the mood to cuddle up all cozy!). A large piece of art above the futon couch can make it feel less heavy and more balanced in the space, and this is also nice because you can convey any mood you want through art or photographs! But I would say to make sure the art has colors that compliment the throw pillows.
Adding an area rug can also will help soften the futon. Another idea is to style the shelves with more light colored items to contrast the dark brown. If you check out the recent Beauty Room makeover I did for Patrick Starrr (see here!: http://mrkate.com/2016/10/01/beauty-room-makeover-patrick-starrr/) you’ll see just how many colors you can use in one room!! Get inspired by that!!