By default, the HistogramCriticalColor is red ( RGB(255,0,0) ). The histogram-chart shows the critical part for the bar ONLY if the HistogramCriticalColor is different that the HistogramColor property. Use the HistogramCriticalValue property to specify a critical value. The critical value is interpreted differently based on the HistogramType property. For instance, if the HistogramType property is exHistOverload, the critical value represents the count of cumulative bars since if the HistogramType property is exHistOverAllocation the critical value represents a percent value. Use HistogramRulerLinesColor property to specify the color to show the ruler in the left part of the histogram. Use the HistogramGridLinesColor specifies the color to show the grid lines when the HistogramType property is exHistOverload. 

The following screen shot shows the critical part when HistogramType property is exHistOverload, and the HistogramCriticalValue property is 3. The bars over value 3 gets colored in red. The grid lines are shown and the ruler shows the count of the bars.

The following screen shot shows the critical part when HistogramType property is exHistOverload + exHistCumulative, and the HistogramCriticalValue property is 4. The bars over value 4 gets colored in black. The grid lines are shown and the ruler shows the count of the bars and the legend of the bars being colored.

The following screen shot shows the critical part when HistogramType property is exHistOverallocation, and the HistogramCriticalValue property is 100%. The bars over 100% gets colored in red. The grid lines are NOT shown and the ruler shows the percents.

The following screen shot shows how the histogram curve is changed once the user resizes or moves bars (  in this case the HistogramType property is exHistOverAllocation )