You left out a link to the image chart.
The API colors all bars, columns, lines, etc by series, so the solution to getting multiple colors is to put your data into multiple series. If you then set the "isStacked" option to true, your columns will look as if they were from the same series. Note, this does not work if you already have multiple series for your columns and you don't want them stacked. Search this forum for multi-colored bar charts - the same principle applies - there are several examples available for making this work.