css

/* <color> values */
column-rule-color: red;
column-rule-color: rgb(192 56 78);
column-rule-color: transparent;
column-rule-color: hsl(0 100% 50% / 0.6);

/* Global values */
column-rule-color: inherit;
column-rule-color: initial;
column-rule-color: revert;
column-rule-color: revert-layer;
column-rule-color: unset;

html

<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>

css

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