On a rainy spring day like today, combining navy and green seems like a weather appropriate color combination. I am not sure what kind of tie I would wear in this kind of setting. There is oddly a fair amount happening with the navy and green, despite both being basic colors. It is simple on paper, but when you take it all in together, it already feels very full. It doesn't need anything else. A unique combination because of this. A tie could obviously work, but often it's best to keep things simple.