it's the most reliable tell that the LW is white.
"my black coworker and I..."
whiteness is pretty consistent in this way! ppl of multiple heritages who email often say, "i'm half-Chinese" or "my father is Mexican"...but won't say what the OTHER half is, as if it's a *given.*
i think @eveewing said this but: having a white parent doesn't make her "half-white" any more than having a father made her "half-male."