Keeping your composite rotor blades painted is crucial to protect carbon fibers from ultraviolet (UV) rays and other sources of damage. Missing or peeling paint can also cause a slight imbalance of the rotor blade, which should be corrected through rebalancing the blade.
Scratches in the paint may reveal grey surfacing film that resides on top of the carbon fiber. Seeing grey is a good sign that the black carbon skin underneath was protected from whatever scratched through the paint. Conduct a tap test around the area to confirm that no damage occurred to the skin. If the tap test is good, proceed with touching up the paint.