Little Sweet Betsy (Trillium cuneatum)
Trillium cuneatum (Little Sweet Betsy) is a delightful spring ephemeral in rich eastern woodlands. This photo (taken by my gardening companion) shows both the usual purple-flowered plants, along with a relatively-common yellow color morph. He describes this in his new blog Wildflower Ecology.
These are flowers normally enjoyed in 'gardens' in nature; nursery-propagated plants are available, although pricey, as they take 5-6 yrs to become large enough to flower, when grown from seed. If you see cheap (large) plants, they're likely to have been poached from the wild.