The white Heliophila collina flower has spread its four petals sufficiently for sepal tips to be visible in the gaps between them.
The sepals grow in two unequal pairs, one within the other in the bud phase. The outer pair of Heliophila sepals may generally be hooded or thickened at their tips; here the pairs are slightly different, an in-curving tip in the one pair versus a raised marginal band in the other, probably the inner pair. The sepals still persist here, while sepals may fall early in some Heliophila species.
The sepals in picture are creamy compared to the white petals, thicker textured with a hint of hairs on the margins, possibly also on their outer surfaces (Manning and Goldblatt, 1997; Leistner, (Ed.), 2000; iNaturalist).