Right before they bloom they look like paper lanterns, or some mysterious origami.
They come in several colors... a bright white, blushing white (above), a white tinted with a spring green, and several shades of pink. I didn't quite get them all on my walk today.
I think this is the best picture. I am teaching haiku right now and this struck me as a quintessentially haiku moment... the floating white petals, the peeling picket fence... I might have to see if I can actually do something with it. The lilacs are coming next... ah, the smell of spring.