Green is to neutralize the redness on the skin, and beige both light and dark, depending on your skin color, is to cover the imperfections.
My way of using it:
I have some combination tricks when using it. I begin with my eyes.I take my Concealer brush and take some of the pink concealer and make a line from the inner corner of my eye to where my cheek begins. Then I take the yellow concealer and put it under my eyes. I blend them with a concealer sponge. When I'm done with my eyes I start with my face. I take some of the green Concealer and put it on my zits, that are red, I let it dry and then I put the beige concealer on top of the green. Then I start dabbing with my concealer sponge and when I'm done I apply my foundation to the whole face.