I love blue salvia and I use it a lot, and it often comes back the next year (behaves as a perennial). So you want a low-growing, non-invasive, non-yellow or red perennial to go in front of your salvias?

Sweet alyssum, although it is technically an annual, very often reseeds itself. I'd use white, although it comes in pink too. My blue salvias (usually Victoria Blue) grow more like 2 feet tall. I use daylilies, which are very well-behaved and come in a large variety of colors -- you could find some of the shorter varieties, and they would also work behind or among your salvia. There are pretty artemisias that are low-growing with silvery foliage. If you want to do herbs, you might think about lavender -- some of them have silver or white flowers rather than the traditional lavender color, and the foliage is usually a silvery blue color. Other silvery herbs would be curry plant or one of the many other sages (of course relatives of your salvia).

You might consider ajuga, which is a low-growing ground-cover with bronzey-green foliage and pretty blue blooms.

I don't know where in Maryland you live, but I lived on the Eastern Shore for many years and have grown all of the above successfully.

I'm not a big white coneflower fan -- the ones I've seen have not been a clear white but sort of a muddy color.

Another annual that often behaves as a perennial in our area is snapdragon. They are very easy, not demanding or invasive, and come in just about every color you can imagine. Many varieties of varying heights. I have some really pretty pink ones that are only about 8" high, and they overwintered from last year and are now in full bloom.

The great thing about blue salvia is that they look good with almost anything you can think of, since their color is a pure blue -- not purplish.

I live in Kent Island, so it's considered Eastern Shore. :)

Thank you so much for you suggestions.

Yes I don't like the purplish salvias either. I think they're called May Midnight?

I'm not sure about the daylilies. I have the orange daylilies and they are kind of invasive. I don't know if the other daylilies have a slower spread rate or stay compact. I don't like digging out the daylilies. Especially that the roots may cross over to the areas of other plants. If I dig out the daylilies, it will certainly hurt the roots of other plants. Some of my orange daylilies overcrowd other plants, surround them so that I have to move the other plants to give more distance from the daylilies.

I like using black mondo grass or silver lirope grass for contrast or edging something. Or blue fescue-but I think it reseeds?

I love candytuft!

For daylilies, see if there is a pale cream dwarf miniature. Most of the little ones I've seen, especially the rebloomers, are shades of yellow, but if you can deal with a med-light butter yellow, Happy Returns is cute and reblooms well.

Re snapdragons, see if you can find one of the Chandelier or Luminaire series, particularly the former. There are snaps coming into commerce that are cultivars or hybrids of some of the Mediterranean species, and they are quite reliably perennial here as long as they get good drainage. I grow Primrose Vein, but there is also a rose pink form.

Here is a link that might be useful: Chandelier snaps

Thank you all for the suggestions. Like I said, I like pastel colors. So this includes pink or light yellow. The primrose vein looks great.

I am considering Ice Plant with light orange or solomon color for borders. Also I think Yarrows with solomon or brick or light yellow would be nice for the layer behind the salvia.

Any other suggestions? :)

What about dianthus "Bath's Pink"?
It's supposed to be very heat and humidity tolerant. Gray-green almost rosemary-like leaves are evergreen. Spring bloom time is fairly short, but the plants remain attractive. They really need well drained soil. (I have dianthus "Fire Witch" and wish I'd gotten this one instead, for bloom color.)

I like Coreopsis 'Moonbeam' a lot. Pretty mellow yellow, delicate foliage. Yellow irises or lilies? I'm growing Lavatara Barnsley amid some blue flowered salvias, but it still hasn't reached a good size or bloom yet. I think the combo will eventually look good.