Outdoor patio cushions faded- Should I try and use fabric paint?

You can buy new pillows at reasonable prices. Go to Plow and Hearth. They have some lovely ones for under $15 each.

Try covering the whole pillow with another red fabric.

I would dye them with Rit Dye, they have a new formula for synthetics call DyeMore. https://www.ritdye.com/how-to-dye/

Don't buy new try to refurbish what you have. If you cover the cushion you have velcro on end so you can slip it off and wash it or take it inside when the weather is bad.

The fastest and cleanest way to rejuvenate faded outdoor cushions is to recover them with water-resistant fabric shower curtain fabric. Panels are standard sizes, can be found at a reasonable cost compared with 'outdoor upholstery' fabric by the yard, and due to its fairly stiff body, is quite easy to sew. As these panels are already coated with a light backing, the fabric does not fray easily when cut.

By spraying the completed new cushion covers with Scotchguard spray, they can readily be made more water proof.