"He is not wearing an orange hat."
Translation:On nie nosi pomarańczowego kapelusza.
A crucial one, however - sadly - 'ma na sobie' was not taught in this course, so it can only be accepted.
Frankly, "On nie nosi" is not a proper translation of "He is not wearing", but we cannot currently offer a better one. Basically, 'to wear' is among this 1% of verbs that translate differently into Polish when they're in Present Simple or Present Continous. So:
to wear (generally) = nosić, "on nosi" (he wears).
to be wearing (right now) = mieć na sobie (literally 'to have on oneself'), "on ma na sobie" (he is wearing).
For some people 'nosić' seems fine even for 'to be wearing' but I personally treat it as necessary evil in this course. That's not a good translation.