My mother's skin on the upper part of thighs has greenish patches. What could this be? How to cure it?

Greenish patches on the skin could be a sign of a fungal infection such as tinea versicolor. I recommend using an antifungal medication like Clotrimazole cream twice a day on the affected area for 2-4 weeks. Additionally, she can take oral antifungal medication like Fluconazole 150mg once a week for 2-4 weeks to help clear up the infection. It's also important to keep the affected area clean and dry to prevent further spread of the infection.