Neutral Tint is a transparent gray (black in masstone) that is specifically designed to be neutral: not warm, not cool, not leaning toward any other color.
Typically, Neutral Tint is made from a mix of three pigments: PBk6 (Lamp Black), PV19 (any number of quinacridone magenta/pink/rose/purple/crimson shades), and PB15 (Phthalo Blue of some sort).