Aviation Snips are Color Coded for a Reason: Use the Correct One

Cutting curves in sheet metal is difficult. The material is awkward and unforgiving, as well as extremely sharp. There are three types of aviation snips that are designed to make three different cuts much easier.
Yellow handled snips are made to cut in a straight line. They can also cut wide curves and are ideal for flat pieces of metal. Green handled snips are designed to make straight and right (clockwise) cuts and are perfect for right handers cutting duct. Red handled snips cut best straight and to the left (counter-clockwise). You can use any of the snips in either hand but they will only perform well when cutting in the direction they were intended for.