"Matěj does not like pink."
Translation:Matěj nemá rád růžovou.
Your suggestion has no verb. The "likes" construction used in this exercise is mít rád (verb plus short-form adjective). If you want to use nerad, a sentence like "Matěj nerad nosí růžovou/růžové oblečení (Matěj does not like to wear pink/pink clothes" might work, but (a) that also includes a verb and (b) it would not be a translation of the exercise sentence. (I'm a learner, too, so one of the Czech natives on the team may have something to add... or subtract.)