I just changed the lower unit gear case oil in my Honda 2006 9.9 hp and 150 hp outboards. I use Honda recommended oil in both. The 9.9 oil was still gold colored like the day I put it in but the 150 oil was black. It was not milky or grey but black. There were a few small filings on the drain plug and I saw no signs of water in the drained oil. Both engines had about 40 hours on them this year and they both ran fine with no strange noises. Is this normal? Is this something I should investigate further? Have any other high horsepower Honda owners noticed something similar?