The green-shaded boxes show periods of time when the S&P 500 and the DBC are rising together and the blue-shaded boxes show periods of time where they were falling together. The only time that the two were inversely correlated was during the initial market breakdown that lead to the financial meltdown of 2008-2009. Aside from these 6 months, however, there was a strong positive correlation.
But then something happened in late 2011. The stock market took off (on a completely unnatural 45-degree angle I might add) while the DBC languished. The correlation that existed from 2006 to 2011 not only disappeared, it has completely reversed! So either the stock market is right, and commodities represent a screaming, undervalued buy, OR commodities are right and the stock market has whole lot of catching down to do.