As mentioned in #3881 (comment)

If the forced color scheme can be clearly identified as matching a dark or light mode (or any future named color schemes), activating that forced color mode should have the effect of setting color-scheme: <that-scheme> only.

Many of the normal color scheme effects might be further overridden by the forced colors (e.g., scrollbar colors), but the color scheme would provide the correct starting point.

If the author uses forced-color-adjust: none, they would also be cancelling out forced color-scheme related changes (other than those related to the normal color scheme preference mechanism).