Thresholds, a value above or below which data items are considered abnormal or out-of-range, are often used to identify items of interest in a data set. While you can apply a filter to see only those elements above a threshold, often it is useful to see which elements exceed a threshold in the context of your entire data set.
The “Alert: Red” color scheme, accessible through the Color Scheme drop-down on the Data tab, is ideal for threshold analysis. When you switch to this color scheme, all elements exceeding the value of the right thumb on the color slider are colored red; all others are black. This lets you quickly see where your thresholds are being exceeded and helps you to identify clusters which might indicate a problem.