In answer to your last question … surprisingly no. The komala itself is largely uniform in color, and any variations in pelt shade are actually the result of differences in melanin for the individual, rather than in genetics for its entire family.
As for why some komala parents give their children differently colored logs than others, researchers aren’t quite sure, but it’s known that the pink log comes from a species of tree known to produce sugary, perfectly edible sap. For this reason, it’s theorized that pink logs are given to komala that have difficulty eating at first, to encourage them to feed. (The normal variation of log comes from some of the most common trees of komala’s native habitats.)
…how a komala’s equally comatose parents can tell when their offspring is struggling to eat, however, is the part that’s anyone’s guess.