How do I make a printed roller shade?

Have you considered using wallpaper to make a printed roller shade? I would use acrylic if you are going with painted.

This is something similar. Maybe this will help:

https://www.hometalk.com/diy/windows-doors/windows/easy-stenciled-mini-blinds-diy--23587240

I just did a stencilled mini blind using lace. I don't see why you couldn't do this with a roller shade.

https://www.hometalk.com/diy/windows-doors/windows/spray-painted-mini-blind-makeover-39783615

You can use fabric paint, a stencil and stopping brush.

Because it a roller it is stiffened. You make it wet and the fabric crinkles.