Duranta. It gets taller, but it's easy to trim, and it comes with variegated foliage and has lavendar, white, or purple flowers. Are there any lilacs or camellias that would work in your area?

Hardengerbia can really only get as tall as the trellis you buy. But it needs to be cut back some and can get top heavy if you don't.
Mine is on a trellis 8 feet tall and it reaches out and when then get long enough I help it at a lower level and up it goes again.

I have a nice Daphne in such a location. Have in the past had rhododendron and Camellia, which did well but got too tall. Al

What about a Ceanothus? The 'Concha' cultivar might work.

Never mind, I forgot that you need something for full shade. The Ceanothus that like shade are probably all too short.

I thought of Brunsfelsia and Hydrangea, but both are deciduous. Then I remembered that there was an "evergreen hydrangea" that might work, Dichroa. I googled it and it gets up to 6', so it might work for you.

Rhododendrons also get tall and come in purple.

wanda

Here is a link that might be useful: evergreen hydrangea

Camellias, rhododendrons and azaleas are perfectly happy in shade. Of course, if you want six feet tall, you're going to have to spend a lot of money now, or wait several years. Unfortunately, plants which grow in shade also grow very slowly. You could buy a standard (tree form) which would put the plant part at that height and would be cheaper than buying a six-foot bush now (which could be several hundred dollars)
Another option which would be very cheap would be a trellis with morning glories. While they grow best in the sun, they are vigorous-to-invasive, and I bet they would grow there. Plus they come in several hues of purple! They would die in the winter, but everyone who grows them knows they reseed themselves very efficiently and they will grow back forever.

Carla in Sac