This should be easy to implement.
Normally the heatmap shows a color gradient for all scores that are between the thumbs on the slider, like this:

With the 'Highlight outliers' box checked, the entire range between the two thumbs is blank, and only scores outside the thumbs are shown, like this:

This should be easy to implement.
Normally the heatmap shows a color gradient for all scores that are between the thumbs on the slider, like this:
With the 'Highlight outliers' box checked, the entire range between the two thumbs is blank, and only scores outside the thumbs are shown, like this: