Yes, these will work great. They will survive fine in full shade. If you just want foliage, you might try Dusty Miller, which does well in partial shade. Black Varnish Pseuderanthemum would be a nice backdrop color and will survive in partial shade. For something really dramatic, look at Lofos White Lophospermum. They cascade 7 to 10 feet, like the same moist soil and will also do well in partial shade. When not in bloom, the plain green will be a nice contrast to the polka dot plants. Hope this helps. Good luck!

Here is a link that might be useful: Lofos White for pretty drama

Does polka dot plant (Hypoestes phyllostachya) get flowers on them if so what color are the flowers?

The flowers are electric purple. If the hours when the sun is shining on your window boxes are during the hot, late afternoon, this may not be the best plant.