The bark of the Douglas Fir (and other tree species) changes appearance with its moisture content. This picture was made after several weeks of wet weather. (not raining all the time but showers on most days) Every layer gets darker with water, but not consistently. Some, including most of the top layer, get very dark - almost black. A light coloured tree fungus, which blends into dry bark, stays light and is easily seen as it contrasts sharply with the wet bark it's on.
Photography notes:
This image as shown is a crop from the original to remove an out of focus area from the right.
We often use focus stacking to make images like this one since trees are round and typically the lens' depth of field is too shallow to keep everything sharp. However we didn't have a tripod with us on the day this photograph was taken. Fortunately the section of the tree shown was relatively flat.