I have tried new motor oil on wood for outside (I create outdoor sculpture in wood). I think I cut it with mineral spirits My experience is that it will still go grey/black. I think it is from fungus mildew. I was really surprised at that. I have a whole wall full of test panels that are outside, trying different finishes and seeing what happens over time. There are mildew preventatives you can add to finishes, but I have not had much luck with those.
