Review (5/5): You need this if you are pale
I wish I bought this sooner - as a pale person, even the lightest foundations are too dark. This has lead me on a decade-long quest to find foundations that will match, much less one in a formula I like. My favorite foundation is Tarte's BB cream, and I mixed two drops of Zero Minus with it in a 1 Oz travel bottle. Still too dark, so I added a little more and now it matches very well, albeit the undertone is still not right (Tarte runs very yellow) but I no longer look like I have a dark mask on my face. I hope to find a similar product that will allow me to cool down the color - it looks like Temptu has something along these lines.
I would advise that if you use this, you will most likely have to lighten up your concealer as well or it will look like a dark spot on your face. I used this successfully with a Revlon concealer that has a doe-foot applicator; remove the wand, and you can easily add Zero Minus. Pump and shake to mix. I don't think this would work well with a cream or stick concealer.