How lucky you are to have these wonderful native shrubs!* Yes, what you see with the changing of the flowers is the norm.* The leaves will change color in late summer or early fall too.* Most folks leave the flowers on the shrub but you can prune them off whenever you like.* From this site:
"...produces blooms on previous year's growth. As flowers fade, prune back halfway. Prune any crossing, broken, or dead branches. To grow for foliage only, prune back to the ground each year in early spring."
To propagate you can take softwood cuttings before they bloom or do as the above site recommends.* This you can do now.
"Remove mulch and stuff from an area behind or to the side of an existing plant, then gently bend a low branch so that it is in contact with the soil. Set a brick or stone over it to hold it in place, and keep the soil moist. In about two weeks, lift the brick and see whether rooting has taken place. (If not, replace the brick and wait a bit longer.) Cut the rooted branch free from the mother plan and carefully dig up the rooted section, replant it in a shady area, and keep it moist over the fall months. You will have a healthy, blooming plant next year."
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.