In the back of the lamp assemblies there is an air break vent to let pressure in an out. It will prevent water from getting in short of putting the lens under water. I suppose if there is enough humidity in the air and it condenses you could get some fogging. It should go away with the headlamps coming on,when things heat up. However, if it gets too bad, like if you saw that after driving through a rain storm, that would mean a breach in the seal around the lens. That will be covered if it's still under warranty assuming the lens itself doesn't have a crack from a rock. The other thing is if you have changed your bulbs and didn't get the bulb housing back in there properly with the gasket seated correctly, that could cause it too.
If that happened and you haven't done anything to the lens assembly, bulb changes or cracks etc. See if it goes away after driving around with the headlamps on. If it comes back espically after a rain I'd have the dealer look at it, or at least log that it happened while you are still covered.
