Black is recommended for casual slim suits, because it is simple to match and more temperament. You can wear it with some white shirts, or you can use a dark green shirt with white skin. If it is dark and light, it can also be paired with a black shirt.
Wearing black jeans is more casual and sunny, and wearing suit pants will be more mature. Personally, I think it is better for boys in their twenties to wear jeans, and it is better for boys in their thirties to wear suits and pants!
Shoes: leather shoes, black booties, casual shoes (I like men wearing high-top leather shoes very much, I think they are very stylish, and military boots are not bad). It depends on how you like them!
Accessories: watches, scarves, ties (formal ties and Korean casual ties are required). If you are thin, scarves are not recommended.
I hope I can help you! !