Hello, I can understand your concern for black discoloration and itching around thigh. After reading your query it appears to be fungal infection of the area which is known as Tinea cruris. Due to heat, humidity and moisture there is a tendency for the growth of the fungus. It is also seen in person who are bit obese side. So if you are overweight then it can b one important cause of your condition. In my patients with your kind of problem I prefer to give both oral and topical antifungal medications. For oral medications I prefer to give terbinafine and for topical antifungals I prefer to give clotrimazole or ketoconazole ointments or creams. Do maintain good hygiene to present further infection. All the best.