Midnight Rose does really well in sun, and has nice pink splashes on the leaves to boot. Midnight Rose Select is supposed to have larger splotches of pink, but I don't have that one to compare. Raspberry Ice, though not a dark purple like Obsidian, does have dark leaves with silver veining and raspberry pink flowers all summer that the hummingbirds love. Those are the ones I have growing in a mostly sunny spot that have done well for the past couple of years.

Karen

These are some in all day full sun here and they do fantastic. The last two are the burgundy ones I had around my Picea standard whaas. The other 2 are on the south side of the house also but surrounded by concrete to boot. They never stop. I pulled Melting Fire last August and potted it while my new driveway went in and put it back in the ground a couple weeks later and it never missed a beat, even with those constant 90 degree days.
Melting Fire
Stormy Seas
Dark Secret
Prince
Cher