Regardless of how much and how often you flush a diesel crankcase it will usually still have black oil on the dipstick. A fresh engine that has no significant blowby will be your only chance of brown oil on the dipstick.

My daughter's car now has about 7,000 miles on the rebuild, and still has oil that is not black on the dipstick for as long as 1,000 miles or so after one of my hot, overnight oil drains.

In my experience, there are very few diesel engines that will remain in such condition for very long.

Good luck and keep on changin' that oil,