Just going to add all those from Hetalia I can think of, since most characters from the other anime I'm familiar with have already been added.
Spain (Hetalia, manga) - medium
Greece (Hetalia, manga) - medium
South Italy (Hetalia manga) - tanned
Turkey (Hetalia, manga) - medium to dark
Egypt (Hetalia, manga) - medium
Cuba (Hetalia, manga and anime) medium to dark
The Asian nations, including Japan, South Korea, China, Thailand, and Hong Kong are all tanned. Japan and China appear in the anime and are major characters, the rest are manga only.
Taiwan (Hetalia, manga) - tanned
Seychelles (Hetalia, manga... I guess?) Her skin tone seems to change each time she's drawn, but she is an African nation, so probably medium or dark
Other African nations, including Kenya, Uganda, Zimbabwe, Botswana, and Ghana, all of dark skintone, who can be seen in the concept art for the hetalia game. So I guess manga?