Sentence:  Compare the vast difference in scope and beauty between his neat and witty little Classical Symphony and his big , muscular , passionate , and eloquent Fifth Symphony ; or the Love for Three Oranges ( gay as it <WSD>is</WSD> ) with the wonderful , imaginative , colorful , and subtle tenderness of the magnificent ballet , The Stone Flower . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)