Tan color fluid inside top of oil cap on 2002 Ford F-150

I had a Oil change done 2500 miles ago, checked the inside of oil cap and had seen a tan color liquid? What is it

Asked by for the 2002 Ford F-150
Is it tan like new oil color or is it white foam looking tan (coolant leaking into cylinder) and is your coolant level dropping?
It could be just the color of oil that has 2500 miles on it ( clear tan color )
My coolant level has not dropped...
not foam is it due to new oil