One last comment... One task of the oil in a Diesel is to hold soot in suspension. As far as I know, the generation of the soot is independent of the oil being used.
That said, the better an oil, the more soot it will hold in suspension, the blacker it should look. So if the oil is not black, either you did not generate a lot of soot or it came out of suspension (not a good thing) or you have a special filter.
That's where an oil test would help, since it takes out the subjective of how much soot is in the oil.
Also, oils have been undergoing reformulation to work with newer emissions systems. The anti wear additives have been changed in a number of major lubes. I would make sure your motor is compatible with the additive package in your oil.
web page web page Link to quote What is Soot and what causes it?
Soot is a by-product of the combustion process in a diesel engine ù a carbon residue formed from fuel air and moisture in the combustion chamber after ignition. Soot particles are held in suspension by dispersant additives in the oil preventing the soot particles from agglomerating (sticking together) and attaching to the rings, pistons and liners. These suspended particles are what turn diesel engine oil black. When too much soot is generated and the additives can no longer keep it suspended, deposits will form on the rings weakening the seal between the pistons and cylinder liners. Upper end wear to rings, liners and pistons begins and if not corrected, will eventually cause severe lower end wear to the main and rod bearings, crankshaft, camshaft, cam bushing and turbo bearing.
