Depending on what product you use? For instance normally I'm a NC45 but today I wanted to try the Studio Fluid and the MU gave me NW43 and said it's normal to change between foundations because MAC doesn't stay true to it's color system. When I got home I looked at it closer and it looked kinda mask-ish on me like it doesn't quite match my skin color. I want to take it back tommorrow and see if the NC45 looks better. But, I'm just wondering if what she said is true for anyone else.