Thanks, Daisy, Laurie, Sue, Philip and Christine for your responses. I was already thinking about coleus as many might be suitable. Also was leaning heavily on sweet potato vines - have never tried them, but always greatly admired them.
Never, ever even thought of yellow going with white and red!
This would open up a wide range of plant choices. Yellows come in so many shades, but I prefer the warm buttercup shades. Please give me suggestions as to which shades of yellow would go best with deep red and white - as I still have trouble associating yellow with red and white.
Pale lavender also sounds as if it would work.
Please keep the ideas coming - and thanks for your help - much appreciated.