In this problem, we need to answer the question ¿Cómo es tu padre? using two adjectives alto y moreno. First, by using the first adjective, we also need to use an adverb. An adverb is a word or phrase that modifies an adjective, verb, or other adverb. In this sentence, this adverb must modify the adjective alto. So this adverb is muy. On the other hand, we need to deny the second feature of your father, that is, we need to say that your father isn't brown, therefore:
Mi padre es muy alto pero no moreno
Translation:
My father is very tall but not brown
