Thanks for providing some details on your use case.
There is no out-of-the-box functionality in ThingWorx to display colored areas in the background depending on the value of the Y Axis. However, you can apply state-formatting to Label Charts using the Markers ChartType (or Line/Markers, Area/Markers) as shown in the attached screenshot Markers_StateFormatting.jpg.
You could possibly dedicate a certain number of series (= number of colors you want to display) displayed as Areas and then add a Line type series on top as shown in attached screenshot Areas+Line.jpg. This is not what the widget's multi-series functionality is originally intended for and this does involve the creation of Chart data especially for the formatting so I will let you decide if this is something worth implementing.
Another "cleaner" possibility would be to create a custom widget for this : Creating Customized ThingWorx Widgets.
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