Every year at this time I think about the order of spring colors. The yellows come first — forsythia and daffodil — followed by the pink of the flowering cherries and the blooming oaks. If we're lucky and it doesn't warm up too quickly, spring in these mid-Atlantic climes will last six to eight weeks. The light hues will give way to vivid purple and fuschia from the tulips and azaleas. Spring is a three-act play of color. And one of its opening scenes is the willow tree. It is the billowy curtain that sways in the March sun. Push it aside, hear the hum of summer in its bended branch.