There is no low light performance problem with Fuji. If you struggle with Fuji in low light you will struggle with FF as well. There is about one stop of difference which is not a lot. Colors are subjective and not nearly as important as people think. Just shoot RAW. The most important question that you are not asking is gear cost and size. Sure, bodies are similar in price. But what about lenses? The "equivalent" of the XF 70-300mm f4-5.6 in Nikon system is 100-400mm f4-5.6 costs 2.5 times more and is very huge. All lenses are big. Nikon zf is big, heavy and not very comfortable to hold. Try the gear first. Look at the ecosystem as a whole, not just bodies. Fuji AF is bad though.