I think that's a great idea. I don't know how much variety you are going to get in white plants for shade, but begonias come to mind, and there are some caladiums that have white leaves with green veins, and lily of the valley will grow in pots... and there are lots of nice foliage plants for shade. Don't think it would be blah at all.

Don't forget impatiens. And i'm not sure if campanula grows well in containers, but i have a nice white one in the shade. And hostas can be grown in containers, for foliage. Oh, and what about a nice silvery artemesia? Moonflowers, if you can get them to bloom. I love white flowers and have a couple of beds devoted to them.

Spider plants (if you can get some babies and start them now, or cut back and divide up an overgrown plant they'll be a good size by June), silver nettle vine, and what about the dreaded Goutweed?

I would do a container with Millet (my favorite right now) and white flowers like impatiens and alyssum which should really pop. If you need something viney - sweet potato vines are awesome.