Found a patch of these last summer. Verification via slow blue stain. They were delish! The can be confused with Frosts Bolete which stain blue rapidly .
Correct, both are titled, the single mushroom is the bi-color, found near oaks and grassy area, while the set is Frosts Bolete, found near conifers and in clay soil. The Bi-color very slowly stains blue whereas Frost's turns blue to the touch and has a much thinner straighter stalk. Please correct me if I'm wrong.