It is possible that this is just your normal variant, especially if you don't have any other symptoms, but I recommend that you go to see your primary care doctor
if you have not done so already. They will be able to perform a thorough physical examination, ask you questions, and determine whether or not something serious is going on that needs to be sorted out.
To start with, the most common cause of purple nails would be diminished circulation. This is very common in females and is usually worse in cold weather, but not in your case it sounds like. The main thing is to make sure that, if you do have diminished circulation, it is not due to a serious problem like a connective tissue disorder.
Second, cyanosis (blue color) in the nails can be a sign of a problem with the heart or lungs. Again, this would be very unlikely in the absence of other symptoms, such as shortness of breath or chest pain or palpitations.
Finally, high red blood cell counts, called polycythemia, may cause this discoloration.
After performing an examination, your doctor may decide to pursue some laboratory tests if they turn something up on the examination.