A greenish-blue mark on your cheek after an injury is usually a bruise (a small collection of blood under the skin), and it commonly changes colour as it heals. In the first 1-2 days, applying a cold compress can help reduce swelling, and after that, warm compresses can improve blood flow and speed up healing. You can also gently rest the area and avoid pressing or massaging it. Mild pain can be managed with Paracetamol if needed. Most bruises fade on their own within 1-2 weeks, but if the swelling is increasing, the pain is severe, or the mark is not improving over time, it is better to consult a doctor to rule out a deeper injury.