It could just be drainage or even the ointment you are putting on the cut- are you having any other symptoms? Do you have a fever? Is the area hot to the touch? Are you seeing a lot of abnormal discharge- other than the yellow on the band aid? Do you have streaks going down your leg at all? You can always have a doctor check it out, just in case- but if you have any additional symptoms of infection, it's best to be seen in order to make sure everything is healing correctly.