"I wear a black t-shirt."
Translation:Saya memakai kaus hitam.
Maybe it's the Jakarta slang in me, but i would say "Saya pakai baju hitam"
It's often spelled and pronounced like that.
In daily speech it doesn't really matter.
The issue is, the official spelling is "kaus", and not "kaos" (that has another definition).
See KBBI links:
kaus = t-shirt
kaos = chaos