The colours of the aurora are determined by the composition of gases in the Earth's atmosphere, the altitude at which the aurora occurs, the density of the atmosphere, and the level of energy involved.
Green, the most common colour seen from the ground, is produced when charged particles collide with oxygen at lower altitudes (around 100-300 km). Occasionally, the lower edge of an aurora will have a pink or crimson fringe, which is produced by nitrogen molecules (around 100 km).
Higher in the atmosphere (300-400 km), collisions with atomic oxygen produce reds instead of greens. Since the atmosphere is less dense at higher altitudes, it takes more energy and more time to produce red light (up to two minutes), whereas green light can be made quickly at lower altitudes (about one second).
Hydrogen and helium can also produce blue and purple, but those colours tend to be difficult for our eyes to see against the night sky.
Many restaurants serve local food like Arctic Char which comes from the arctic area. Also, meats like bison and reindeer are served as part of traditional meals. In the very far north you can also expect to taste traditional indigenous meals.
No! It is a myth that the northern lights happen only when it's cold. They happen year-round and since there is more darkness to see them in the winter people associate the cold winter with the auroras. August and September is a great time to see the Aurora while wearing a T-shirt and shorts!