With me, I was using Virosol on some window sills to remove dirt, etc, by spraying the window ledges first before cleaning the windows with wfp.
When I was at the ladies front door getting paid, I looked down and noticed the orange spots on the plastic door step bit/thing which was odd as when I cleaned the door, there was no orange spots on the step.
It dawned on me that after cleaning the front door first and when spraying the window sill next to the door, the wind blew some of the spray on to the door step and had dried.
I'd also unconsciously noticed odd orange spots, stains, etc, on other houses and didn't really think anything of it but after that ladies doorstep, I realised Virosol was the one thing in common.
I've tried various things since then to remove the orange marks without any success at all so I'll give bog cleaner a go.