Some of the Nemesia rupicola flowers in picture have dark, vertical lines low down on their upper lips. There are also white (sometimes pale yellow) cushion-like humps on the corollas at the base of the lower lips.
Blooming happens from late spring to after midautumn. The photo was taken in Gauteng during May (Manning, 2009; Trauseld, 1969; iNaturalist; iSpot).