Suppose we wanted to know whether the yellow-green morph produced more seeds than the standard green morph under the best possible conditions. we have data on the average number of seeds produced by each morph in each treatment. which data set would we use?

Based on the information provided, I would surmise that you could use the average number of both to understand which would produce more seeds. Based on the averages of both, of course. And that would give you the answer you would look for. it would take both to know which one produced the most.