column-rule-color

column-rule-color: red;

column-rule-color: rgb(48 125 222);

column-rule-color: hsl(120 80% 40% / 0.6);

column-rule-color: currentColor;

<section id="default-example">
  <p id="example-element">
    London. Michaelmas term lately over, and the Lord Chancellor sitting in
    Lincoln's Inn Hall. Implacable November weather. As much mud in the streets
    as if the waters had but newly retired from the face of the earth, and it
    would not be wonderful to meet a Megalosaurus, forty feet long or so,
    waddling like an elephantine lizard up Holborn Hill.
  </p>
</section>

#example-element {
  columns: 3;
  column-rule: solid;
  text-align: left;
}

/* <color> values */
column-rule-color: red;
column-rule-color: rgb(192 56 78);
column-rule-color: transparent;
column-rule-color: hsl(0 100% 50% / 60%);
/* Global values */
column-rule-color: inherit;
column-rule-color: initial;
column-rule-color: revert;
column-rule-color: revert-layer;
column-rule-color: unset;

<p>
  This is a bunch of text split into three columns. The `column-rule-color`
  property is used to change the color of the line that is drawn between
  columns. Don't you think that's wonderful?
</p>

p {
  column-count: 3;
  column-rule-style: solid;
  column-rule-color: blue;
}