When they wear jewelry, What do the countries (of your choice) tend to favor in metal and gemstone?
What a nice question, Anon! :D Never came to my mind.
My headcanon has a very supernatural base, so the choice of their tastes are based on what they are, indeed. Because they look like people but also they are the storm, the sun, they're an avatar, they're an animal, etc. So they look elements which syntonize with them by instinct.
For example, I see Antonio wearing gold and Gabriel wearing silver; I like the idea of twins/sun-moon/day-night contrast.
Portugal was born from the sea, that is why his eyes has the scent of the ocean and its color; also, is unpredictable. At the same time, he is a quiet, a reflexive and melancholic dreamer; sutile and selective. As the Moon represents un tarot. If I have to choose a gemstone for him: aquamarine and amethyst. He adores that gemstones.
Sun, on the contrary, is pure light, joy and eternal playing. Giving life without precaution. The mirror of the Moon, but the contrast of the complement. That is Antonio: lots of noise, lot of kids, lots of fiestas, lots of love, lots of everything. That has consequences, too. Geamstone: Ruby. Pure fire.
That's why they're rivals with Arthur: they're pretty much the same. They wanted the same goals, the same people, the same amount of things, the same obsessive ambition. By the way, England is like a sunrise, pretty shiny but with some darks parts (I mean Antonio has them too, but they're not defining him). Geamstone: Emerald, like the Forest he was born.
If you want to know more about other characters and my headcanons with them about this, just ask Anon! I don't want to do this eternal to read, because I talk too much XD