The CSS Gap Decoration spec defines the following color-based CSS properties:

1. column-rule-color
2. row-rule-color
3. rule-color (which is a shorthand for the first two)

column-rule-color is already noted as being handled by Forced Colors Mode, so the proposal would be to add row-rule-color and rule-color to the list of properties affected by Forced Colors Mode, as well.

CC @kbabbitt