I've heard the same thing about yellow, though all of our experiences point to it not being an exclusive requirement. The salvia that the bees loved in my garden was white or purple. They also went for the Russian sage in a pinch.
Steph, thanks so much for the offer! I'll make a note to contact you in the spring. Trenton is about an hour north of Dallas, in Texoma close to Oklahoma. I'll take the passionflower, nepeta (catmint?), whatever you're givin!
