Any new unusual mark or mole should be checked out by a GP. It may well be an easily treatable skin condition but it's best to get it examined in case it's something that needs further investigation. You don't say how long ago you first noticed it. Have you been bitten on your leg that you remember (in the garden or on holiday) as this can sometimes cause a hard spot (dermatofibroma) that can be mistaken for a red, grey or blue mole.
