There're a few reasons your SPOT may never turn purple, one of which being that you're doing a great job putting on your sunscreen and are protected! Another popular reason you may never see it return to purple is because you're not facing SPOTMYUV to direct sunlight to do a SPOT CheckOther reasons could be a low intensity of UV in your region at that time or other environmental conditions.If your SPOTMYUV started off purple, and it turned clear, then we can guarantee you that it's working. Please contact our customer support email (info@spotmyuv.com) for any questions or problems you've experienced.