I just saw this on ... HGTV Color Splash.

Start at the bottom with your darkest color.
Paint the 2nd color, but take a dry brush and cross hatch the darker into the light.
When you go to the next stripe, use a clean brush so you don't take the darkest color higher up on the wall.

This lady on TV did it with dark orange into a bright sunny yellow. She was mimicing a sunrise.

Good luck!
C.

okay but I wonder how the sweeping of the brush worked, what if the paint is already dry?

She cross hatched it.

She called it a dry brush, but she did it after she painted the 2nd stripe across the wall. So it had a few minutes to dry a bit.

Experiment. Ya got nothing to lose. It's only paint.

C.

I would talk to the store where you buy your paint about "open time." This is the time between application and drying. The longer the open time, the wider the window of opportunity you'll have to mess around with the paint. If it dries too fast (like Ben Moore Aura does) you won;t be able to go back in and work those borders between colors. You can buy an extender to add to paint to increase the open time.

Good luck! I tried my hand at decorative painting years ago and the learning curve was steep for me.