What do rotting or saturated areas of shakes and shingles appear as on the roof?

Rotting or saturated areas of shakes and shingles typically manifest as dark patches on the roof. This darkening occurs because water infiltration induces deterioration and decay of the materials, leading to mold or mildew growth which darkens the surface. As the wood becomes saturated with moisture and begins to break down, it loses its original color and takes on a darker appearance, making these areas easy to identify during an inspection.

While light patches may indicate a difference in material or reflectivity, and wet patches could suggest currently saturated areas without the inherent signs of decay, it is the dark patches that are most indicative of underlying rot and damage. Cracked patches signify physical deterioration but do not necessarily indicate moisture saturation or rotting. Hence, identifying dark patches is crucial for assessing the roof's condition and recognizing potential issues that need addressing.