This house has aluminum siding. The corners have this dark dirty appearance. Is this just dirt, or can it possibly be mold?
They probably used a butyl caulking that seemed to have a lot of an oil type product for viscosity. It seemed to creep and attract/hold dust.
Looks like dirt and dust o me Mike.
I agree with Brian,I’ve seen it several times
Needs to be resealed.
I am sure it is both. Some caulk, butyl included will grow mold or mildew. I would not sweat that one.