Community
https://knowledge.autodesk.com/support/3ds-max/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/3DSMa...
If you have enough geometry this is the tool your looking for, previous to 2016 you could find a one line script to enter a hex color to get the selection, but now it's a tool. Had to use it on terrain to cut out a coast edge and make a sea wall.