Colored granules on your roof coverings are what protect the roof coverings themselves from the elements.  This is why it’s important to NOT pressure wash your roof as doing so can lead to granular loss and reduce the roof’s life expectancy. In fact, I’ve seen newer roofs completely destroyed by pressure washing (treatment with zinc granules is the most common way to keep moss off your roof).  Pictured here is substantial granular loss and exposed underlying fiberglass underlayment.  These roof coverings were in poor condition, clearly due for replacement.  This was discovered at a recent home inspection on Orcas Island in the San Juan Islands.