I’ve noticed several plants, ‘Nova’ and ‘Prairie Moon’ among them, show more yellow coloration in cooler climates than here in the Midwest. Even my mlokosewitschii could hardly be described as yellow.  The foliage shows its macrophylla heritage.  Formerly named Olga. Silvia Saunders commented it “sets seeds well”.

‘Nova’ used to be carried by several nurseries, but at least one has recently discontinued this cultivar. 

Cultivar: Nova
Year: 1950
Seedling No: A strain, seedling numbers 16946-16958
Parentage: 17B: F2 of (mlokosewitschii X macrophylla)
Flower: Color: creamy white (listed as pale yellow by some)
Form: single, 2 rows of petals, crinkled edges
Blooms: Week 4
Carpels: at least 2, green
Stigmas: pale yellow
Disc: [DISC]
Stamens: yellow filaments, abundant stamens
Plant: Habit: upright spreading
Foliage color: medium green, glossy
Foliage form: large leaves
Height: 30″ (reported)
Recommendation: Recommended
Availability: Few specialty nurseries