I Fell On A Fast Moving Treadmill And Have Sustained

I fell on a fast moving treadmill and have sustained friction burns on my knees. They are the size of a 10 cent piece on both knees. They both scabbed up, scabs have now come off but my knees look unsightly due to new skin, round purple/pink circles. Can you please tell me how long they will take for the skin to go back to normal colour and what treatments are available