Shalom U’vracha! It is said in the Halacha that one should wear white clothes on Rosh Hashana. 1. Does this regard only the shirt or the trousers as well? 2. If this is the Halacha, how is it that we see so many Bnei Torah wearing black suits on Rosh Hashana?

This is not the Halacha, it is a preferred custom. 1. If possible, white trousers would be appropriate, but again, this is only a preferred custom. 2. It is known by the Rishonim that a black outfit causes the heart to surrender and the person to distance himself from sins, so this is probably the reason the Bnei Torah dress this way. This question was answered by Rabbi David Hai HaCohen