Somewhat related to #2204987: Option to reset to theme defaults?

A potentially useful option would be to allow a preset to not set a color for a particular rule, since all rules are included in every preset. Sometimes the underlying theme provides colors that are good enough, or sometimes one does not need colors for every rule and wants to avoid setting arbitrary colors that might mess up future elements on the site.

I'm thinking something like a checkbox next to the rule setting on a preset that says "Do not set a color for this rule" and would disable the color picker and input field.