Crocus tommasinianus -sometimes called the Woodland Crocus- doesn't mind growing in a bit of shade but the flowers only open wide when the sun is on them.
 Petite they may be but they provide a beautiful dash of colour early in the season, seeding themselves around and also multiplying by cormlets (i.e. new corms forming on mature corms).
 The colours of the petals range from lovely silvery violet to rich plum purple but they all have a bright orange stigma and anthers dusty with pollen. "Tommies" are a magnet for insects braving the cool spring days.