The Loop Cut & Slide indicator line (in the 3D viewport, in Edit mode) changes color with some themes, so it has a setting in Preferences, but I haven’t been able to find it. Also checked the Preferences part of the 3.0 manual, no joy.
Here’s some examples of a proposed loopcut on the back of Suzanne’s head in four of Blender’s included themes:
Should be simple, right? Edit > Preferences > Themes > 3D Viewport, it’s gotta be one of the color controls that’s yellow in the default theme (Blender Dark), black in Blender’s Maya theme, and blue in Blender’s Modo & XSI themes. But I’m not finding it.