Do you have an idea of height you want to reach? Bushes might need moving in a few years as the trees get large.

I like flowering bushes myself, trying to get a variety going so there is some bloom here and there, over the season.

Some old standby's might be good. Hydrangeas, now in MANY flower shapes, various sizes, blooms linger for a month or more. Reliables are Annabelle, Tardiva, PeeGee, in my colder area. Limelight and Pinky Winky is getting good reviews, not sure on Z4. You could check the Hydrangea forum here on GW for other suggestions.

I have Fothergilla, lovely early Spring blooms like brushes. Comes in larger bush 4-5ft and a dwarf about 3ft tall. Has GREAT fall color, orange to red. Good contrast to the pines.

For smaller, Tree Peonies have beautiful flowers in spring. Can be slow starters to grow, but I LOVE the dinner plates size blooms. Wild colors that Herbacous Peonies don't have. Again, nice color to the leaves on some. They can get up to 4-5ft over a longer time.

Rose of Sharon, Althea, come in many colors, bloom over a long time in late summer. I think they are hardy in your area. Come in singles and doubles, grow taller pretty quick. Can be pruned yearly to keep smaller if you want.

Snowball bush is pretty tough, has long lasting white balls of flowers in later summer. Another old faithful one. Gets up about 6-7ft. Can't remember the fall leaf color.

I have some Elderberry bushes, pretty lacy leaves. They took about 3 years to get going well. They grow about 8ft tall, have very LARGE white, lacy flowers. They then grow lots of berries the birds enjoy, or you can pick because they are edible. I shear mine off every spring, they come back and reach that height again. They do send out some runners, but easily controlled with lawn mowing.

Fruiting bushes are attractive, plus you can get the berries. Currents are pretty, short with round leaves. Have funny green flowers as spring breaks, then the red berries. Birds will eat berries if you don't. Short-bush Blueberries should work in your zone, have berries AND flowers, along with terrific fall color. High-bush Cranberries have flowers and berries, nice fall color.

Mine are all green leafed year around for our horses. Vet said to avoid colored shrubs, not sure of the dangers yet. Hope these are helpful ideas. We get cold, but are on the WARM side of the Lake!

Any of the ninebarks would work. I doubt that a purple smoke will prove hardy to you--even in zone 6 a hard winter brings a lot of dieback. Not sure any of the beautyberries (Callicarpas) are hardy to zone 4 either.