Decorate a plain natural-fiber rug inexpensively by adding a border with stencils and stencil paint, or spray-paint a rug, using masking tape and newspaper as a resist. Cover areas to remain unpainted with masking tape -- large areas with taped-on newspaper -- and spray-paint to create borders and stripes.
A highly patterned natural-fiber rug can be painted with indoor/outdoor paint. Just brush paint on patterned areas to make a design.
Protect painted-fiber rugs with a clear sealer, applied to both sides of the rug, to prevent the colors from bleeding through to the floor or carpet beneath. Natural fibers can be very slippery; place a piece of nonskid fabric under the rug.