There are a couple of choices at the nurseries linked above.

Bishop of Llandaff ( sold by Plant Delights) is red – sometimes leaning slightly toward orange. It’s probably your best bet if height is important; it’s among the tallest of the named dark leaf varieties. The alternative is Bishop of Auckland, available from both Plant Delights and Corralitos. Auckland’s flowers are a deeper red and the foliage is very dark, but the plant is a bit shorter than Llandaff and unlikely to hit 4 feet (although you never know).

Leo – Congratulations on your success with the hollyhocks and poppies, plants that germinate well and start growing early when given a cold spell. They’re great candidates for fall sowing, so I’m not surprised to hear the winter porch trick worked out.

But if you have snow, you don’t have the right climate for sowing dahlia seeds outdoors. Dahlias aren’t hardy north of zone 8, and that’s just the limit for mulching the tubers and leaving them in the ground. The seeds need warmth to sprout and the plants need warmth to grow, so if you want to give them a head start you’re stuck doing it indoors.

Bramble – glad you enjoyed the photos. All I can say about powdery mildew is that my dark leaved dahlias have never had any – not the slightest trace. They’re in Maine, which is more flower-friendly than NJ, but the many dahlias I grow in NY, where conditions are somewhat more like yours, have never had any mildew either. Given that the NY cosmos, phlox and other mildew-magnets are not infrequently disgusting I’d say plant type probably trumps leaf color. If your other dahlias have been healthy I’ll bet the dark leafed ones will be too.

Do you think the seeds would respond to winter sowing? I had wonderful luck on the back porch (outside, uncovered) last winter — with hollyhocks, California and Iceland poppies.

Best,

Leo