When you have related elements in the foreground of a chart, arrange them in a darker-to-lighter pattern from the bottom of the chart, upward. This “Earth-to-Sky” pattern is the way we view color naturally; that is, from the earth to the sky.

The earth is darker than the trees, which are darker than the sky, which is darker than the clouds. 

So, when you have related foreground elements that may use different colors, you should choose an order of those colors from darker to lighter.

 Keep in mind that the elements must be related to one another, as in a group.
 

 
For example, in a segmented vertical bar chart you can use the darker-to-lighter Earth-to-Sky pattern for the segments within each bar.

If there were three segments per bar, then the bottom segment would be darkest, the middle segment a bit lighter and the top segment the lightest.

If the top segment had been the darkest color, the chart would appear top-heavy.

 

When displaying clusters of bars, choose a darker-to-lighter pattern starting from the left-most bar in each cluster.

Don’t use the “piano-key” approach by putting the lightest color between surrounding darker colors.

When looking at a related set of items from left-to-right, or from bottom-to-top, the eye scans colors more easily when the arrangement is a dark-to-light pattern. A faster scan gives the audience more time to listen to the message.

 Since the order of the colors can make a difference, why not use this to your advantage?