I want to purchase two of the dark blue plumbagos. From the pictures on this site some look darker than others but the latin name seems to be the same for all the pictures. What is the name for the one which has the dark blue flowers, rather than the light blue?
Can you post a link to the pictures you're referring to? Assuming you're referring to Plumbago auriculata http://davesgarden.com/guides/pf/go/414/ I've never seen one in real life that's dark blue so my suspicion is the pics look that way because of the lighting or the camera that was used to take the picture. There's another plant though with the common name plumbago which does get darker blue flowers--Ceratostigma plumbaginoides http://davesgarden.com/guides/pf/go/876/
I'm not sure how to post a picture that is already on the website. The two I've looked at are PlantFiles: Picture #7 of Plumbago, Cape Leadwort (Plumbago auriculata) and PlantFiles: Picture #15 of Plumbago, Cape Leadwort (Plumbago auriculata).
You may be right about the light for these pics. However we have seen a darker blue plumbago here in Houston on occasion. As our two light blue plumbagos are gone since our freezing cold winter this year, we want to replace with the darker blue ones which we enjoy more.
RE: the invasiveness of plumbagos. I love it. It grows and blooms and blooms.
If I'm looking at the correct pictures, I think it's cameras and lighting causing most of the difference you're seeing. It wouldn't surprise me if some are slightly darker than others, but none of them are going to be what I'd call dark blue. It's also possible there are some cultivars that tend to be a little darker in color--here's the list of ones that are in Plant Files. http://davesgarden.com/guides/pf/b/Plumbaginaceae/Plumbago/auriculata/cultivar/0/ It's hard to say from these pictures which ones might be darker because of the camera/lighting issues, but you could ask at your local nursery if they know of a cultivar that is a little darker. Or else keep going around to your local nurseries when they're blooming and watch out for ones that have the color you want.