It’s nail polish. Makeup artists at MAC counters use the colors on the ends of their brushes to differentiate between everyone’s brushes and their own. I painted mine before I was hired to work for MAC because I thought it was cool. It doesn’t really serve a practical purpose unless you mix your brushes a lot with others and want to keep track of them.

Studio Fix Fluid
Studio Fix Powder
Trace Gold Blush
Dollymix Blush
Anastasia Eyebrow Pencil
Wondergrass Eyeshadow
Vanilla Eyeshadow
Humid Eyeshadow
Shade Fluidline
Lime Dandy Glitter Liner
Plushblack Mascara
Lure Lipliner
Vegas Volt Lipstick
Pink Lemonade Lipglass

USED:
Studio Fix Fluid
Mineralize Skinfinish Natural
Anastasia Perfect Brow Pencil
Electrosky Paint Pot
Frozen White Pigment
Violet Pigment
Poison Pen Eyeshadow
Carbon Eyeshadow
Blacktrack Fluidline
Plushblack Mascara

Fafi Eyes 1: Vanilla, Hey, Pink Venus, Howzat
Blacktrack Fluidline
Plushblack Mascara
Anastasia Brow Pencil
Lure Lipliner
Skew Lipstick
Flusterose Lustreglass

Studio Fix Fluid
Mineralize Skinifinish Natural
Bare Study Paint Pot
Jest Eyeshadow
Cranberry Eyeshadow
Espresso Eyeshadow
Anastasia Brow Pencil
Blacktrack Fluidline
Fascinating Eye Kohl
Plushblack Mascara
Pink Treat Lipliner
Syrup Lipstick
VIVA GLAM VI SE