If you are a Civil3D user who likes things to turn blue when selected (the default for selected objects in AutoCAD 2015 and later), yet also wants to be able to see what corridor region is being selected, the answer is in the Corridor Feature Settings. (See image below.)
From the Settings tab of the Toolspace, right-click on the Corridor Group and select Edit Feature Settings. Then expand out the Region Highlight Graphics, change the region highlight color and also increase the lineweight.
That’s it. It’s easy when you know where to look.
See also, TIP #4431.
Notes from Cadalyst tip reviewer R.K. McSwain: A good find in the wealth of Civil 3D settings. This will certainly help other Civil 3D users out.