is there a way to set the color of the Klaxon light? setting the lights color seems to have no effect on it? is this somehow encoded into it's nif?

nevermind... seems you can set it by setting the objects emittance

You can just be careful as if you pick an exterior one, it will be a different color depending on the time of day. (for most exteriors like CapitolWastelandBorderRegion)