On my diesel Jeep Liberty, they run the blowby back through the engine. Turns the oil jet black after 20 miles.
An assumed cause and effect, likely erroneous. How do you know the blowby is the cause?
Some formulations of oil simply change color due to getting hot, multivis oil additives, if I recall correctly, changes from translucent amber to translucent black, with no deleterious effects. Heat changes the light reflection/filtering behavior but not the properties that the engine needs for lubrication.
If the oil takes on soot particles (or any particulates), it is no longer translucent, whatever the color.
This, BTW, is why testimonial claims about a product often have little value, as they are not based on science or repeatable test results/definitions.
My cousin's, friend's, daughter got some of that oil on the back of her ear and got pregnant the next day. Therefore, the oil must be a good pregnancy aid.
Perfectly rationalized cause and effect, right?