I've had it happen before on concrete a 2% mix with greenwash will release the purple stain just like algae or mold but you might have to scrub it if it dries.
Wishing a hearty thank you for all of your replies!
I got it off, but not the way you'd think.
My irrigation water is gravity fed. I set the sprinklers and hoses, and depend on water pressure from the ditch, but sometimes it is stronger than others.
I also try not to hit my house, fences or sheds, but sometimes we have unexpected pressure.
Water pressure increased and hit my house all Thursday night, and I have a big clean area where the purple once was!
Mean time, I will try to make the Plant Wash not so colorful, and will try to remember to rinse non-plant surfaces with clean water before it dries.