The usual flower color of Pinguicula vulgaris, the common butterwort, is purple.
Pinguicula vulgaris is a small perennial carnivorous plant in the butterwort family, Lentibulariaceae. Its funnel-shaped flower rises above a basal rosette of sticky leaves, which trap tiny insects and other organisms. The flower is generally purple, making it easy to distinguish from the plant’s often green foliage.
The flowers are typically at least 15 millimetres long, and the plant itself usually reaches only about 3–16 centimetres in height. It grows in damp habitats such as bogs, fens, and swamps, often in low or subalpine areas with limestone or alkaline conditions. Because it experiences cold winters, it survives the unfavorable season as a compact winter-resting bud called a hibernaculum.
Purple is the fair quiz answer, but it is not an absolute rule. Some plants or recognized forms produce white flowers, including Pinguicula vulgaris f. albida, while bicolor forms combine white and purple. That variation is why “usually purple” is more accurate than saying every flower is purple. The green, red, and yellow options are not the normal flower color for this species.