Learn Spanish (Spain): El diseñador quería que la colección fuera innovadora. - The designer wanted the collection to be innovative.

This is the sequence of tenses in action. Because the triggering verb in the main clause, quería (wanted), is in a past tense, the subjunctive verb it triggers must also be in the past. Therefore, we use the imperfect subjunctive fuera rather than the present subjunctive sea.

The English translation uses the infinitive "to be". Why can't we say quería la colección ser innovadora?

In Spanish, verbs of desire like querer only take an infinitive if the subject remains the same (e.g., if the designer wanted to be innovative himself, it would be quería ser innovador). Because there is a change of subject here—from the designer to the collection (la colección)—you must use que followed by a conjugated verb in the subjunctive.

Could I use fuese instead of fuera in this sentence?

Yes, absolutely. The imperfect subjunctive has two sets of endings: the -ra endings and the -se endings. fuera and fuese mean the exact same thing and are perfectly interchangeable here, though the -ra form is generally more common in everyday spoken Spanish.

Why does the adjective end in -a (innovadora)?