What is this black coloring in attic?
To my untrained eye, it does appear to be mold. The would indicate a moisture problem. The first place I would look is bathroom exhaust fan vents, they need to exhaust outside of the house, through the roof or out the siding, not into the attic space. Next I would check for ventilation, often in the form of soffit and ridge vents, but could also be gable vents. They need to be unobstructed. If neither of these appear to be the cause, then there could be a leak in the roof.

With any moisture sources solved, the typical remedy for the mold itself is a bleach solution, being careful to not get it on your skin, clothes, or anything else that could be damaged.