All (or most) manga/Toriyama costumes

[Marco Polo]

6 - GOODBYE SUIT - For Trunks' return to the future, Gohan dressed well, wearing a simple but stylish suit, with a cool black arm band as a special touch.

I don't think the black arm band is worn for coolness... I think it's worn as a sign of mourning for Goku's death (the other character in this pic also wears one).

[SaiyaJedi]

I don't think the black arm band is worn for coolness... I think it's worn as a sign of mourning for Goku's death (the other character in this pic also wears one).

That's correct. It's a standard part of attire for mourners in Japan (it shows you're in mourning, even when you're not wearing black).

[Cold Skin]

The description of Gohan's black arm band has been corrected accordingly, thank you for the info, guys!

Not knowing of this accessory's actual meaning, I did think it looked cool since it broke the otherwise very classic style of the costume and brought an additionnal, unusual touch.
But now that I know what it's for (meaning NOT a deliberate choice to customize your look but a much more serious reason), I removed the "cool touch" mention to describe the arm band's real meaning instead, of course.
Plus, since it's about mourning, it would really feel out of place to have something like "plus it looks cool!!" when it's not meant for that and is obviously something nobody would be eager to wear given the circumstances implied...

[UltimateHammerBro]

A black arm band to show mourning while not wearing black isn't exclusive to Japan though.