Maybe some type of ornamental flowering crab with purple leaves? Sorry, I don't know any specific cultivar but I believe there are a few.

Maybe a shubert chokecherry? They have pretty purple leaves as well.

For golden trees maybe a golden catalpa 'aurea'.

There are probably more but these are the few that I know of.

Glen

Prunus cerasifera 'Newport' gets only 18' tall and 15-20' wide at maturity, and has purple foliage. 'Thundercloud' is about the same.

Although not dark-colored in leaf, many of the deciduous saucer magnolias (Magnolia x soulangiana) look stunning in front or at the corner of white houses. Just make sure you choose a violet-pink blooming cultivar for most effect--such as 'Lennei' or 'Verbanica', 'Alexandrina' or 'Rustica Rubra'.

Crabapples are grand, too. Do ask for a selection that is rust and scab resistant so your tree looks super in summer and fall.

Even if you choose a non-purple leaved accent tree, you can have purple-leaved shrubs to anchor your planting beds around the white house's foundation--sand cherry, leuchothoe, fringeflowers may work, not sure this last one is hardy in zone 5 though.

I have a 'Makamik' crab that I love. The foliage is dark and it has gorgeous deep pink flowers in spring, not to mention that the fragrance is awesome! It does have fruit but it really isn't a messy tree. I don't know how tall you want this tree to get but the Makamik grows to about 30-40'high and just as wide, according to Lois Holes book. We've had it 10 years now and it is still only about 15' and rounding out nicely. Marg

I agree about the Shubert cherry. They grow to about 15 ft.