The phrase "the Color Line."

The NYT has an opinion piece titled "Cousins, Across the Color Line," about present-day Americans of different races who trace their ancestry to the same white person, for example, those who see themselves as descendants of Thomas Jefferson.

At one point, Gayle [who is black and considers herself a descendant of Jefferson] asked me [a white woman who also considers herself a Jefferson descendant] if I was looking for absolution for what my family did, and we both agreed the word was imperfect. I think instead we are both looking for some present-tense reconciliation. We acknowledge our desire to feel connected to our shared history, and appreciate the fact that we can sit together, looking at the mystery of the past and trying to articulate what it means....

There is something radical in knowing Gayle....

The author, Tess Taylor, doesn't use the term "color line" in her text, though she does mention  reaching "across racial lines." The word "line" is also used in the essay to refer to ancestral lines, but put that to the side. I want to examine the inference, in the headline, that if a black and a white person today are connecting, they are crossing something called "the color line."