If you have any of the Logitech keyboards.
You can assign a key light action on any of the light up keys.

It's not totally accurate, but pretty close.
By this I mean..
Press the mapped key, and step 1 will turn the light on, amongst other things.
And step 2 will turn the light off.
But there's nothing which is saying, this is active therefore the light is on.
It is more, the last step I was on either turned the light on or off.
But that is a good warning or visual check of the state.