Ukraine

I think it went a bit further than just selecting the right paint.

I remember there was a program to enhance the stealth for relatively low flying surveillance aircraft (still mostly propeller aircraft at that time) and one of the most effective measures was painting the underside of the plane White and then illuminating it on purpose with a light that was matched to the sky. The light was usually bluish to match the sky. https://en.wikipedia.org/wiki/Yehudi_lights

The reason why this was not simply done at night was of course that the surveillance equipment needed some light to work :)