Diagram colours!
Please, please, please could you stop to consider just how many red-green colour-blind people there are out there? Mine isn't severe, but there's just no way I can compare the silly little blobs of colour that are the "key" to the diagram with the chart above. I mean, what the hell is wrong with red, yellow, black and blue for crying out loud?!
A significant proportion (roughly 7%) of the male population and about 0.5% of the female population are colour-blind. Have a heart, please...
And go look at www.vischeck.com to see how your charts look to someone with red-green colour-blindness!