I am very familiar with color theory for makeup correctors thanks to my Bobbi Brown Corrector in Light Peach that does wonders for my purple tinted under eye circles, so I (foolishly) thought that I would just pop the NYX Green HD concealer on my face in a similar fashion. Straight from the doe foot applicator, I dotted green concealer onto my active breakouts and drew sheer parenthesis around my nostrils. I started blending as usual, using light tapping motions, and found all of a sudden the product was gone - blended into nothing. I gave it another go, this time with my trusty Real Techniques Deluxe Crease brush, and found far better results. I did get coverage with this, and it did mask a fair amount of redness, but at a cost I didn't anticipate - a deathly grey pallor.
Now, I admit this was mostly user error. After playing with this product (in the evenings with no pressure to get to work on time, of course) I figured out there is a razor thin line - use too little green concealer, and it will blend into nothing, but use just a dab too much, and you will get an odd grey cast that is even trickier to fix than the redness. The challenge in this product is the undertone and shade. Bright mint pastel green does not blend into skin easily because it doesn't contain any pigment components that are naturally found in my skintone (or maybe anyone's?). If this shade were less bright or pastel, or if the undertone was more yellow or olive, the pigment would look more natural and wearable on the skin.
On days that I do use it, I use a synthetic pinpoint concealing brush and slowly add product onto an angry breakout. I set lightly with powder and then cover with a pigmented concealer that matches my skintone. This three step process works just fine, but it is time consuming and the result only looks mildly better than if I didn't use a green color corrector.
Overall, NYX HD Concealer Wand in Green is marginally better than having no green concealer at all.