Wow, a month with no reply! I can't promise you the best foliage but I can suggest a cultivar with nicely shaped dark green foliage. Rimpo/Rinpo.

Here's a shot from early spring when it still has a nice reddish tint.
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All my pictures show the flowers and not the foliage so good, so here's a shot from when I bought it.
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Paeonia decomposita

paion, link went to French language site the gave a detour.

I only wish I could read more than a few word in French and most of those are food terms.

I do like Tria for Autumn foliage and colour.