This comes up frequently on the Rose forum. I did a search for "perennials" and got these results.

Here is a link that might be useful: link

I love this little groundcover, lysimachis nummularia:

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As you can see it is a beautiful color, it is very shallow-rooted and doesn't take much for itself in the way of nutrients. It makes a lovely, low carpet, and it maintenence free. I use it a lot.

If it's flowers you're wanting, then I recommend a mini-daylily called Eeny Weenie. It's only about 10 inches tall and has a profusion of little yellow flowers on it.

Lainey

Short veronicas or salvias perhaps? I just bought Salvia nemerosa 'Marcus' which I've put more or less in front of my roses. Hope it works out well!

Janet's Garden

Last night I visited a garden where the roses were underplanted with a tall pink Heuchera with plain green leaves --- I'm guessing some older variety. It was truly lovely (and I don't even usually like either plant!) Also, a boxwood border around them.

Blue would be a great color companion for both pink and apricot. Catmints are ideal, easily grown, long bloomers. Walker's Low, the standard favorite, might get a little too big especially given the rich soil conditions that roses like. However, there is a wonderful small staure catmint, 'Little Titch', that is a richer blue-lavendar, much more compact (15" tall by 20" wide) that would be ideal to cover the roses naked legs.

Geraniums are also great but most would tend to get a little too big.

One thing to check, though there are short English Roses, many here with good culture will get bigger than the british sources say. So your 36" rose may end up a foot taller if the culture is good. Then you don't need to be so worried about height, anything in the 2' range, which would cover most geraniums and catmints, would be good.

If you want a white companion that makes an excellent shrubby 15" mound from May through July, and is a cloud of tiny white flowers from July to October, try Calamintha nepetoides. Few plants in the garden flower as long or look as pristine throughout the entire garden season.

I have Lamb's Ears in front of a pink rose and Veronica Georgia Blue under another one. The Georgia Blue is a lovely blue before the rose blooms and remains a very low, airy groundcover throughout the season and it does rebloom at times. I use both throughout my beds, and I love both. I have Walker's Low by another rose, but I think it may be too high. If you can find a lower variety, I think that would look nice, too.

I don't know where I read it but I think Parsley is planted at the feet of roses for some reason.

My parsley stays green nearly all winter and has an airy type leaf that always looks nice. It gets to be between 12 and 15 inches.

Wow thanks for all your ideas. They are all so great!!

An under-planting of chives is supposed to deter blackspot (presumably because of the sulphur content) - but it didn't work for me, nor did it look attractive, except when the chives were in flower. If possible, I'd choose something that thrives in the same soil conditions as roses (i.e. something that likes a rich, even heavy, soil) and also something that can handle the overhead shading from the rose itself (yes to parsley, then!)

I'd agree with the Heuchera suggestion, but I think that instead of plain green, bronze leaves could work really well. It could enhance the green of the rose foliage while picking up the apricot/pinky tones of the flowers. Also, using a foliage plant would mean that you wouldn't be distracted from the rose blooms.

Low-growing Geraniums also come to mind, but I can't think of any flower colours that would look particularly good with those rose colours. I don't think blue or purple would work, and pinks might just clash...

There's a brilliant book by Tony Lord called "Designing with Roses" (see reviews on Amazon), in which he talks about underplanting... Unfortunately I can't remember any of his suggestions, but will look it up when I next get a chance.
http://www.amazon.com/gp/product/0711217149/qid=1149763246/sr=1-2/ref=sr_1_2/102-6002517-5100128?s=books&v=glance&n=283155

Not just under but over and around.
This is the Austin rose Eglantyne with Dr Ruppel clematis, achillea and adenophora in front.
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Autumn Sunset with petunias.
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Peace with pink petunias
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For something really different, I've seen Palace Purple heucheras suggested in a gardening magazine. They can take full sun and the contrast in growth habit, colour and leaf shape should make an interesting effect.

Janet's Garden

I have catmint, salvia, geranium biokovo, Johnson's blue geranium, sweet allysum, ajuga and annual verbena and petunias planted under my roses. I would highly recommend any of those.
Kathy

For roses with taller stems, I have sweet woodruff growing around them. Woodruff has shallow root systems and the roses thrive. It's a spreader, so I pull out clumps each spring as needed, but the flowers are beautiful with the roses.

I plan on getting 2 salmon colored shrub roses and was looking at black viola's to underplant. will the roses supply enough shelter from hot sun for the viola's to thrive?

I've seen artemisia and allysum, and I thought those were beautiful. The silvery/white made the whole planting seem a little magical.

In the past, I've used salvia "Blue Hills," which was sooo very pretty -- it's a true powdery blue more so than lavender -- but you have to be mindful of the bees. They LOVE that stuff.

Later in the season, geranium "Roxanne" started to replace the salvia, and it was gorgeous. I planted it under a red-pink, a pure pink, a yellow, and an apricot and it went with each one. Under the yellow, it looked a little more blue and the foliage stood out a little more; under the red-pink, the little bit of purple-pink in the eye of the geranium came out. Lovely. I can't wait to add more, especially under my white rose. Highly recommend it. I've read good things about the fragrant geraniums, too. It might be nice to get one with rose-scented foliage for a double delight.

Also, you might want to consider a little blue ornamental grass -- I tried one of this, too. It was pretty under the apricot, but a little too deep for what I was looking for otherwise. Maybe it'll work for you, though.

Right now, I have nepeta, agastache, & purple fennel. For a lower edging this year, I'm going to try alyssum, lambs ears, & calamintha nepetoides. I also had several salvias last year(leucantha & guaranitica), but I don't think they overwinterd.