Hello, I have a purple beanie which is a 3D item and everyone ingame is seeing it purple but for me it appears black.

What can I do about that ?

What version of Toribash are you on? I use 4.9 and I see odd 3D item colours for items made after 4.9.

I'm using 5

I'm pretty sure the beanie was made after 5.0

Updste your Toribash to the latest one. If by 5 you did mean the latest one, then mess with your graphical settings.