The Galloway lab published a new paper on variation in petal color in American Bellflower in Frontiers in Plant Science. They found that abiotic conditions shape geographic-scale variation in the intensity of petal reflectance while genetic structure is the strongest driver of petal color as perceived by its pollinators. You can read this new paper here.
Koski, M. H. and L. F. Galloway. 2020. Temperature and historical colonization shape geographic variation in petal reflectance and coloration. Frontiers in Plant Science 11: 991.