What kind of colonial timeline do you want. Similar to OTL? Or do you want a (significantly) larger German colonial empire? In that case you need a pre Napoleon POD. I would even go so far to say you need a POD around 1600 or even earlier. In 1800 the good colonies (the Americas, Indonesia, India) were already taken, while Germany wasn't even unified at that point. Germany simply was too late to gain a respectable empire. It can't compete with Britain, France, Spain, Portugal and the Netherlands. The only thing left were scraps.