If you’re reading this, chances are you’re looking for roof-cleaning tips because your shingles are no longer looking new and attractive. If your roof appears dark and discolored in some areas, you may think that mold has developed on the surfaces of the shingles. However, the black streaks you’re seeing are really colonies of blue-green algae. If you’re noticing thick, green patches on your roof instead, then you’ve got a moss problem, The north, west, and shady areas of your roof are most susceptible to these moisture-loving nuisances.