Answer: The one that is a compound sentence is "I painted my bedroom beige, but my sister painted her room blue".
Step-by-step explanation: A compound sentence is a sentence made up of two or more independent clauses. Unlike dependent clauses, independent clauses, which are joined by means of a coordinating conjunction, can stand alone as sentences because they express a full thought. "I painted my bedroom beige, but my sister painted her room blue" is a compound sentence because it includes two independent clauses ("I painted my bedroom beige" and "My sister painted her room blue"). They have been joined by means of the coordinating conjunction "but".