While tasting for doneness, I noticed that it had practically no spinach flavor. In the meantime I prepared a simple sauce of melted butter, the ricotta, snipped fresh chives, freshly ground nutmeg and salt. I finished the cooking as directed and drained the linguine. In the colander they did smell of spinach. I then emptied the pasta briefly into the pan with the warm sauce, and mixed.
Alas, the spinach taste had disappeared again. Even worse, despite having been properly prepared, the pasta was not al dente, it was downright gummy. It's possible that adding additional ingredients to pasta interferes with the final texture.
This will probably be the last time I buy flavored pasta.