Stencil Paintmask which can be applied to the rear of the Seat. Once adhered, you can use fabric paint and a brush to paint it on. Spray paint may work as well but best to test first.
Dimensions of Design are 127x64mm
Dimensions of the Stencil in total are 148x82mm
If seat covering is PVC, a multi surface water based paint should work and the stencil has to be removed when the paint is just touch dry but still soft.