Condensation most likely if everything else checks out okay. Clean it out and follow up later.

 

^^ I agree. This can easily happen if you drive a short distance without letting the engine warm up all the way. If everything else is the way it is supposed to be (oil and coolant look fine), you should have nothing to worry about.

I have seen this on my truck a few years ago after only driving around the neighborhood.

Just keep an eye on things for a few days and see how the oil looks.

 

Humidity, fog ect can contribute to this. The PCV system draws air from the intake prior to the throttle plate. Low level in the coolant reservoir, plus a cold air intake (none OEM or no airbox) will pulling steam/vapor, since it doesn't have cool down.

A thorough oil change will tell you how contaminated the oil is.

Like mentioned above its typically condensation on the cap..

 

Like the others have said possibly condensation etc.

Does the oil on your dipstick look like that too?