Yes, aren't empty spaces way too tempting??!?!?

How about a burgundy coral bells to pull out the burgundy of Silver Scrolls? Midnight Rose looks like a potential candidate. The foliage being similar and the color being complementary might make for "tie-in" affect you are looking for.

ANother one of my fave groundcovers is Sedge "Treasure Island". It's quite short not like Ice Dance. But I'm not sure if the variegation would help or hurt. One well-rooted plant can make oodles of new plants.

I have H. Green Spice (kinda sorta similar to Scrolls) in a spot with a Hosta Halcyon nearby. They seem to complement each other well. Not sure if that's what you are looking for. THe large leaves might calm down a lot of diversity.

Cornus Canadensis? I have some in an area that has totally taken off. It is definitely tie-ing everything together. But I hear that it isn't always so happy with siting. It really really really likes it where I have it. It's just regular green.

nan, what about ophiopogon/black mondo grass?or carex hobb's blue...or a dk ppl sedum?
mindy

Lamium m. Purple Dragon might work--has silver in the leaves. I picked it up for a friend from Santa Rosa Gardens' end-of-season sale and potted it up when it got here. It has grown quite a bit and looks very healthy. Not sure it would fit the bill but worth checking out.

Choc. Chip ajuga? Potentially aggressive, but will definitely fill in.

My Purple Dragon Lamium goes nuts. needs regular control. But pretty.

How about run-of-the-mill lamb's ear?

How about a burgundy coral bells to pull out the burgundy of Silver Scrolls? Midnight Rose looks like a potential candidate. The foliage being similar and the color being complementary might make for "tie-in" affect you are looking for.
Although you have gotten some really good ideas already I think Wendy is spot on. In my mind there is nothing better in companion planting then when one plants accent color is the other plants primary color. For example grouping daylilies I will often pair one lily with a chartreuse eye with another lily with a chartreuse body.
I would suggest you throw one of your H. Silver Scrolls in the car with you after leaving work early (after all you have a mission) and visit all of your nurseries until you find a good match. You will know it when you see it. Oh it just dawned on me this is going to look fabulous with your house color.

I like salvia n. 'Caradonna' with my purple and silver heuchera, along with "cherry bells" campanula (very grapey in color but a super aggresive thug, beware!) and a low green with red hints groundcover sedum. The salvia is definitely a totally different color but the gray foliage is really nice there and I like the purple/blue pop.

I forgot -- 'lady in black' asters -- nice purple-y foliage, kind of see thru so good toward front of beds, with that nice fall bloom....

OMG, what a lot of great ideas. I'm going to need to widen that bed (just a few more feet!) so I can try out a few of them.

I do worry that more silver foliage will accentuate the slightly yellowish foliage of the old rhody; a straight purple-leaved plant might go a long way to counteract the problem. (Maybe I'll eventually figure out how to eradicate the black vine weevils that have ruined that foliage, but meanwhile, in THIS lifetime, just solving the clashing problem will be a big step forward.)

I have a really nice dark purple heuchera, with sort of mitten-like, rounded leaves, that might fit the bill nicely - maybe I'll divide it and give it a try. Also lots of Palace Purple, in some very crowded beds, that should be moved anyway.

Mindy, I've never seen mondo grass survive here, not sure why - maybe the winters are too wet? But the color shape of the foliage would be an excellent contrast. I also have some dark purple sedum, Postman's Joy, that might fit the bill - another good idea, and this is a nearly full-sun site, so it could be a good place for it.

Lady in Black aster - what a lovely plant! I've never seen that before, but it looks like another good option. Maybe I'll also add some of the zillion thalictrum Black Stockings seedlings to the back of the bed - they've popped up everywhere - while I'm at it, for more coordinating purple.
Thank you all - lots to think about here! I'll post some photos when it's done.

have you tried nematodes for the black vine weevils? The weevils are a soil-living insect. I have used the Bonide imadiclorpid (sp) soil drench myself on rhodies with excellent results. I find it a bit more palatable because it is not a spray. pros and cons for sure.

Maybe some Hollytone will green up your old rhody coloring.

I find purple-leaf plants solve a variety of design issues. They just seem to go with nearly everything.