There's been an option for a few versions to show relative rather than absolute in counts. It works best with percentages disabled, but can be used even with percentages.
If you enable this option, then for example, on a level that requires you to save 40 lemmings, initially the IN will display as "-40". When it gets up to 0, it means you've reached the requirement, and a positive number essentially means "this many lemmings more than required". In this way, it's similar to how L3D handles this, except displaying the number as negative rather than as a different color.
The option in question is disabled by default; you can turn it on on the config menu (F3 on the title screen).