Our local Dahlia club has published its own color charts to help classify
the flowers. A member showed me these charts, and curiously there were
pages devoted to the color I used to call purple. When I pointed to those
colors, the dahlia person assured me that there were no dahlias in that
color range.

They do use the term purple, and when I asked the dahlia person to show me
a dahlia in that category, a dusky red one was pointed out. Oh, well...

Another member mentioned Dahlia 'Purple Joy' and said it was a very
distinctive lavender which really stood out in a planting of dahlias.