A compound subject is a subject made up of two or more simple subjects that are joined by a coordinating conjunction and share the same predicate. In the sentece above, the compound subject is NP "yellow and black". This compound subject has been linked by the coordinating conjunction <em>and</em>.
In this sentence Yellow and black would be the compound subject. Yellow and black are both subjects and the use of the word 'and' lets you know it is a compound subject.
