I sent a message to Vintage Gardens to see whether my Jazz Club (not) is actually Geant des Batailles. Gregg said the photos match and the description matches, but its vulnerability to disease would be the clincher. He said Geant can't hold its leaves for even a week in Sebastopol without spraying. This mystery rose of mine is no more prone to black spot than anything else in my garden, so I guess I have to keep looking for an ID.
This is the photo he thought looked the most like Geant, and it probably is the truest depiction of the color. If I go to his garden again, I'll take a blooming sprig with me and try to match it to one of his plants.
