I can't think of any. Any advice appreciated. Thanks.
The only shrub that blooms for me continuously from early summer until frost is my potentilla fructosa "Pink Beauty". Maybe other potentillas would also, but this is a nice compact, mounded 2' shrub. Covered with pink blooms when temps are 80 and below; flowers turn to cream above 80 degrees but revert to pink again as the temp goes down. (We had only one day above 80 last summer though so I'm remembering the color pattern from the two summers before that.)
There are several shrub roses that will.
Beyond this and potentilla I don't know of any others.
Knockout shrub roses will bloom, repetitively, throughout the growing season.
Oh, yes! I love my knockout roses that are in part shade. They bloom in Albany, NY from the start of the season all the way to November if given the chance! They come in a variety of colors. I love them for their floriforousness (is that a WORD?) & the fact that Japanese beetles don't swarm all over them--too much.
For a splash of color all year long you could also try a variegated shrub with both flowers and berries. A variegated redtwig dogwood works well for me, such as Ivory Halo. It is smaller than the species and so it can be used in foundation plantings. I also like Carol Macke Daphne, mine seem to flower lightly and intermittently after the spring flush. No berries or red twigs, but the leaves hold their color well into winter. And then there's the fragrance!
My Lady Banks rose blooms pretty much all season from sometime in June until after first frost. Hydrangea 'Endless Summer' starts blooming early July and blooms through light frosts until I get a hard freeze. Both these plants have very visible flowers.
I also have a Daphne x transatlantica 'Summer Ice' that is blooming now (this is an unusually early spring, but it does usually bloom with the daffodils) and will bloom until hard frost. It has small clusters of little white flowers and subtle white edges on the leaves. It's not a 50 MPH plant, but one you want where you will walk by it to see the flowers, the lovely leaves, and enjoy the scent.
Another way to extend your season of bloom for a shrub with a short bloom season like a lilac, is to plant a clematis a few feet away and train it into the branches of the shrub so that the clematis blooms appear among the leaves and branches of the shrub. Many of the type 2 and 3 clematis have a relatively long bloom season.
I have Kerria Pleniflora growing under the pine tree where it gets only morning sun. It can be grown under full sun, but thives in light shade. It blooms early spring and then re-blooms summer till early fall. It has golden yellow double flowers (approx 1" dia), very pretty foliage and architectural features.
After 10 years or so, It has achieved maximum height of 5ft, base width is approx 3' (widened up by suckers). It's hardy to zone 5 and may die back in colder region but grows back (mine never died). It requires well drained average/normal soil. Once established, I never watered it. (My zone is 6bCanadian, USDA 5). Hope this info helps.
A couple houses ago, I had a hydrangea that would bloom late summer, into fall. I do not know the variety, sorry.
Oh, I misread your post. You want full season color....
Try Annabelle Hydrangea. Mine usually start flowering in June and last past frost. Typically, you leave the flower mops on them till late winter and they flower on new growth