If you worry that white will look too stark, take a cue from Marcelo Brito Design, who jazzed up a pair of chairs with white slipcovers using matching patterned throws. The look is casual yet coordinated.
Superb idea to add the dark graphics and the frames above. When color change is wanted, all they have to do is change the chair covers and the frames. Since the chair covers are not fitted, they can be several yards of fabric tucked in with no sewing needed.