I bought this basic pillowcase and pillow insert from Ikea. While it's nice and big at 26" across it's also boring to have a plain white pillow. So with some painter's tape and fabric paint I made this striped circular gradient effect.
Step 1: Prep pillowcase
To get the pillowcase ready, I put down several pieces of painter's tape across it like in the picture here. I also put a piece of cardboard inside for a better painting surface and to prevent paint from bleeding through to the other side.
Step 2: Paint!
There wasn't too much planning here. I poured out some black and white fabric paint on cardboard and mixed it up to get a few different hues. I then kept painting onto the pillowcase for a circular gradient effect.
Once the paint is on, let it at least dry to the touch before removing the tape.
Step 3: Stuff it up
Once the paint has completely dried you can stuff the pillow insert inside and prop it up in a nice place to sit. For better long-term use, and the ability to wash the pillowcase, iron the pillowcase to heat set the fabric paint.