I had a Perkins 4-108 on our previous boat and the oil was always black. If you got it on your fingers it took days to wear off. The engine on Tropical Dance is a Perkins 6-354 with 6,000 hours and 25 years on it and when it's changed (between 100 to 150 hours) it's still got some transparency to it. No black at all, only a used oil look.

I don't understand it but I like it.