You can describe something that's flawless, without a single mark or spot, as unblemished. In magazines, models often look like they have perfect, unblemished skin — but it might just be airbrushed.
Clear skin can be described as unblemished, and so can other things that are unmarred by visible flaws or blotches. You can also use this adjective figuratively, for anything that's clean or untainted, like your unblemished driving record or a sports team's unblemished record of wins in a season. This latter sense of "unimpaired morally" is actually the original definition of unblemished.