Several years ago, I was working on a small room for a designer show house. My space was a former upstairs sun porch that had been enclosed to make a guest bedroom. The existing roofline was both slanted (for rain run-off) and low, running from 7 feet 6 inches on the high side to 7 feet 2 inches on the low side.
I painted the room a light, sunny lemon yellow and extended the wall color onto the ceiling six inches, making a yellow "frame" on the ceiling. I added a crisp, white, narrow wood molding at the line where the "frame" ended, and painted the remainder of the ceiling a yellow-tinted white.
Thanks to these techniques, which made the walls appear six inches taller, as well as some well-chosen furnishings and artwork, people viewing the room tended not to look up. They assumed the color change signaled where the walls and ceiling met. The proportions of the room appeared larger, and tall people stopped ducking when they entered the room.
My solution worked so well that visitors didn't notice my tricks, so I started pointing out the room flaws and how I'd fixed them. A few visitors recognized my problem-solving abilities and hired me for their homes.