You expose a second, more specific, value. Then provide a useful fallback for when you set the old generic value. If you have a multicolored backlight, then a u

You expose a second, more specific, value. Then provide a useful fallback for when you set the old generic value. If you have a multicolored backlight, then a user of the old abstraction just wants white. If there's multiple backlights, you could just dim them all. This is what an abstraction is. The abstraction doesn't need to cover all possible cases in the future. You just have to pick what that abstraction will mean for your new thing when you have it.