Blue = pump timing or just wore out. (even a bad turbo will cause a little bit of blue)
Black = overfuel, either normal under boost or volume/rack setting wrong.
Grey= pump timing, chain stretch, bad nozzles or several other little things.
All this is dependant on engine temp, overall running (skips, fuel knock and so on), mileage and so on.
Just as a example, my cummins smokes blue cold, black as sin under boost and on long idle will blow white on accel. None of this is a problem, just the nature of the beast in its current state of tune (250hp750torque)
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.