ThinkOrSwim: How to explain the coloring scheme of bar charts

In your second link there's a a chart titled "Bar Breakdown". On each bar, the left horizontal line is the Open and the right horizontal line is the Close.

Look at the chart immediately above the "Bar Breakdown". If the right horizontal line (the close) is higher than the previous bar's close then the bar is green. If they are the same then the bar is gray and if lower, red. This is defined under Algorithm:

A bar is shown in the "up-tick" color if the current close price is higher than the previous close. Conversely, if it is lower, the bar is displayed in the "down-tick" color. If these are equal or if the bar is the first on the chart, the bar is then shown in the "neutral-tick" color.