A product that I have used for literally 30 years is JOMAX. A quart of Jomax is combined with 3 quarts of bleach and 4 gallons of water to make 5 gallons of solution. It is a detergent, a bleach activator and mildicide. When used, black mildew and green algae will disappear before your eyes. It is relatively mild. It has never damaged surrounding plants etc. when I have used it. I use this product evey spring to clean the gunk off my exposed aggragate patio here in Portland where algae is the State Plant I simply flush the solution away with a brisk power washing.
Another product which might be useful is Behr's All In One Deck Cleaner. This is basically oxalic acid with enzymes as cleaners. It is an excellant concrete cleaner. I discovered this by accident, having spilled the solution on my driveway while using it to clean my cedar fencing. The spilled on area looked like new! So I just did the rest of the driveway. It also did a great job of removing the rust spots from the sidewalk where I stupidly did not get the iron containing fertilizer pellets off the walkway.
After a thorough cleaning, I don't know why the pavers could not be treated with concrete stain to return some of the color.