Pressure
washing.

Concrete and siding hold on to more than people realise. Mildew, algae and road film build up slowly enough that you stop noticing, until a clean strip turns up next to it.

Driveways, walkways, patios and porches get washed until the original colour of the surface comes back. Siding gets the same treatment at a pressure the material can actually take, because blasting a house at full pressure does more harm than good.

It is the cheapest thing you can do to change how a property looks from the street, and it is quick.