The Arverni were a Celtic tribe that inhabited the present-day region of Lyons, France.
The Arveni were a very powerful tribe living in the Auvergne. Their most important stronghold was Gergovia (somewhere near Clermont-Ferrand). The most notable Gallic resistance leader, Vercingetorix, came from the Arverni. They had been the most powerful Gallic tribe in the 3rd and 2nd centuries BC under their king, Luernios, However, when his son, Bituitos was defeated by the Romans in 123BC and the Roman ‘Provincia’ (that is the origin of the French word "Provence") was established, their ascendancy passed to the Aedui and Sequani.
averni they seem to be similar colour to the mantle border.
The rhinophores and gills certainly don't appear to be fl to me, the rhinophore clubs are brownish but the gills are certainly nearer the colour of the mantle edge.
averni, and I think your lower two photos show a link between that brown form and the more usual colour form with a red or orange-red border.