You need to get the images used by the sample. They are all 1x1 images that are stretched to the proper sizes. You can get a zip file containing the ones I use as well as a few other colors from here.
Why are all the bars one color?
You can change the colors to any ones you want to make an image for. I've seen people do it based on the values. ie: lowest 25% gets one color, 25 - 50% gets another, 50 - 75% get another and 75 - 100% get yet another.
You can really do it however you want. Even assigning a new color to each one isn't difficult and the only real problem is that you don't know in advance how many colors to create. The graph can handle hundreds of data points and maybe I'm just lazy, but I didn't want to create that many different colored dots!
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