I’ve had blue lights that black sharpie could not dim.

The solution for those is black nail polish. Dirt cheap, easy to apply since it’s more of a goo than a liquid which you apply it by a brush that comes with the bottle, and it’s completely impervious to any sort of light shining through in one coat. If you’d like some light to see if the thing is on or off, apply a thinner coat.

It completely solved my aggressive LEDs on things problem.