Take a look:
https://www.google.com/search?q=engi...ih=556#imgrc=_
There are several examples of this waxy yellow build up, and it happens with all engines. The reason seems to be short-distance driving in cold weather. Condensation mixes with the oil creating this substance.
I take 20+ mile drives everyday, and the weather is cold. I noticed today a tiny smidgen of this yellow stuff on my oil cap.