gseaplot2 color bar meaning unclear

[abartlett004]

I am confused about what the the red and blue rectangles in a gseaplot2 graph are supposed to signify. Looking at the source code of gseaplot2 and gsInfo, it seems as if the width of the rectangles is meant to signify the number of genes on the ordered list required to accumulate each decile of my gene set, but in reverse. I cannot think of what biological or statistical significance such information might have, particularly after it has been reversed and plotted on the same x-axis as the cumulative enrichment score graph. Could anyone advise me on this?