Marsh Blue Violet (Viola cucullata) 2016-4-25 Newark, DE

-petal bases are darker than Common Blue Violet (V. sororia)
-is variabe - blue, blue-white, white-blue
-the hairs on the beard are clubbed
https://www.minnesotawildflowers.info/flower/marsh-blue-violet
"The lower spurred petal is beardless, has darker blue veins, and is typically shorter than the two lateral petals."

Northern Bog Violet (Viola nephrophylla) is similar but doesn't have clubbed hairs and the side petals point forward
https://www.minnesotawildflowers.info/flower/northern-bog-violet