Last week in a car museum I saw a Lincoln Sedan Delivery Deco Liner, with a Harley Davidson. In a bright dark purple. The car was out of reach, but such an ink color might not be. Searching online I found Diamine's Imperial Purple. Beautiful and bright, especially in a broad and web nib. A bit too much for the workspace, but excellent for all sorts of personal writing. The color is pleasant to read, which makes it suitable for personal notes and correspondence.
I found the ink a bit more dry than usual from Diamine, but other than that the ink behaved very good. The shading is phenomenal. No feathering and negligible show-through. Water makes an instant mess of the ink, be careful.
Compared to other purple inks this is by far the most saturated, bright and dark purple. Montblanc's Lavender Purple is more red. So is Herbin's Larmes de Cassis, and much less saturated. The closest match is Améthyste de l'Oural (Herbin 1798, shimmer ink). That ink is darker and less bright.
Imperial Purple is a good color to have in the collection!