Mmh, i think they use Petroleum, but not all Buoys are equipped with Lights. In the War there were less Buoys than normal, but i dont know.
An other Problem is, that they can used different Painting as today. I didnt find anything about that in the War.
But i think its o.k. to use green and red, so that anyone who drove an Uboat into the Port of Kiel, in Real Live know what to do in an Emergency Situation.
@Budds: i edited my last Post if you miss the Aswer of your Question.