I honestly like what you said. I have also been using dirty and clean bitcoin without reasoning much about it. Could it be the name the government and exchanges gave to victimise people.
After reading your post I understood that I may have bitcoin sent me from untrusted source, although the bitcoin was not used to commit crime but to ensure privacy I decide to mix the bitcoin. By this, that bitcoin in the address is called dirty or tainted as the case may be. I prefer using the term you used "Breaking the trace".