I have this wall in house. I painted it over 4 years ago when I was 8 months pregnant with my first child, but that's a story for another day. Since then, I have been asked countless times how I did it, so I figured I should probably share a tutorial on it, so I have something to reference people to.
My wall started out the light tan (the smallest stripe), so I only needed to paint the two greens. Pretend my wall is all the light tan. Start out by taping off the wall as you normally would for painting (baseboards, ceiling, etc.). Now determine how wide you want each of your stripes. Mine are 9", 6.5", and 4". I went along the wall making small pencil marks for 15.5", then 4". The 15.5" will make sense in a bit. Then comes the taping. The trick is this fabulous instrument known as a laser level. You set it on the ground and it displays a red LED light on your wall. Line it up with your pencil marks and once the bubble shows it's level (meaning your line is straight), don't touch it. (Sorry the picture isn't that great...see that little red line on the right of the dark green stripe)? Then I used good quality painter's tape (THIS IS A MUST!!!!) and taped along the red line. Repeat all across your wall one red line at a time. Then I painted the 15.5" pieces the lighter green. (This picture was Photoshopped to demonstrate). Repeat all along the wall. Allow paint to dry. Then you pull out your laser level and painter's tape again. Measure the 6.5", display the red LED line on your wall, and tape. (See why you MUST use good quality painter's tape? You don't want to pull off that light green you just painted). Go ahead and paint your dark green in this area. Allow to dry, remove all your tape and you are done! I hope that made enough sense without being able to show you exactly how it was done! If you have any questions, please let me know!!!!