They wouldn't have known about monitors per se but I know what you're saying, GUEST, about the use of individual colors juxtapositioned to create the same sort of perception of overall color that the brain perceives from signals transmitted by the retina.

I have to point out, though, that Claude Monet and Georges Seurat went about creating this perception in markedly different ways, and were leaders of two different (though related) artistic movements. Monet, of course, is the archetypal Impressionist (in fact, "Impression: Sunrise" gave Impressionism its name); Impressionists tried to portray visual reality accurately in terms of transient light and color. Georges-Pierre Seurat was the founder and leader of the Neo-Impressionist movement known for using Pointillism (a.k.a. Divisionism: a technique of painting tiny, detached brush strokes of different colors); pointillists were less concerned with realism than with illusion (such as portraying linear structure without lines).

But artists of both movements were pioneers; if they hadn't dared to think and paint in a way that defied centuries-old assumptions about the way we see, we might have had to wait a lot longer for the monitor and the pixel to be part of our everyday lives.