The Correlation. Correlation is a measue of how close the line fits the points that you found in your experiment. Anyone can say whether they think the line is a good fit or not, but to measure it exactly, we use the correlation coefficient: R2.
As the seasons change and the amount of sunlight decreases, less chlorophyll is produced, and the leaves appear less green. Chlorophyll is broken down into simpler compounds at a constant rate, so green leaf color will gradually fade as chlorophyll production slows or stops.
Or they should, anyway. While leaves will always change color as the amount of sunlight wanes, several weather conditions can affect how brilliant they become. High heat or drought can rob leaves of their brilliance, or make leaves drop early. Insufficient rain in September can also hurt peak color.