I would say, in my opinion, that most if not ALL of the perennials with foliage described as "purple" are not really purple, but in fact a bronze-green, bronze, burgundy, or dark beet reddish.
It depends on many conditions including moisture, sun or shade, and time of day one is viewing the "purple" foliage.

The only foliage I would call purple is that of some wandering jews, or Setcresea pallida 'Purple Heart', and Strobilanthes dyerianus or Persian Shield.

Sedum Bertram Anderson has gorgeous purple foliage in full sun. It's a short kind - not groundcover, but not tall like Autumn Joy either. And it's hardy in my zone 5 garden.

Strobilanthes and wandering jew are true purple, but not perennial in this zone.

Thanks for the good suggestions. I may end up with one of them--have grown most of them at one time or another. But none are perennials here and that's what I'm still hoping for. I appreciate your replies.

Salvia Lyrata 'purple volcano' has been perennial for me and it re-seeds generously.

Becky

I've not grown it myself, but would you consider perilla more purplish? I believe it self sows and rather aggressively.

Some ajugas? I keep seeing new cultivars that catch my eye. but I shy away cause of that aggressive thing again.

You are right about the aggressive nature of these two. And perilla looks more burgundy to me. Still hunting....

ginny,
as a big affectionado of colored foliage I have observed that amount of sun, coolness of air, age of the plant makes a big difference on color or the leaves coloring. I just had seed grown polemonium Purple Rain and geranium Purple Haze which were absolutely unbelievably purple colored earlier in the spring turning to interesting purple tinged now... and Am thinkin you might have to settle for something less definitive...
Good luck though!

I'll second (or third?) the Setcresea pallida 'Purple Heart' and Strobilanthes dyerianus or Persian Shield, but they're tender.

There is another plant with the same metallic purple (in spots) as Persian Shield, but the leaves are 4" to 5" wide and shaped like maple leaves. Would anyone know what it might be called? It is tender, too.

As I said, sedum ba IS perennial in zone 5.

I was looking at my Heuchera 'Obsidian' yesterday and it had a strong purple tone. Of course, very dark, not like a purple flower. Its claimed to be black. And not every leaf had the strong purple tone and not both sides of the leaf and probably not all year long, can't remember. But perhaps the most purple of the heucheras.

Could the perennial name you're looking for be Cryptotaenia japonica atropurpurea, Sharon?
Zeph