A good tight engine running properly won't carbon up the oil in a hurry. I've seen cars with several thousand miles on them with only slightly dark oil. It only means the oil is holding up nicely and not collecting carbon, so the engine is running properly.
The oil I drained out of the 280 SE (years old!) was only dark, not black.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!