The Green Gold by Winsor and Newton is one of my usual choices because it is so useful and interesting in mixes, makes gorgeous glowing whites and is also really good for glazing. It is a transparent oil paint with excellent lightfastness, and very soft and buttery.
I am not sure how I stumbled upon this colour but it appeared in my kit soon after I started in oil painting and was largely ignored for a while as I explored the more obvious choices. One day I mixed a little of this deep vibrant green with titanium white and was surprised as the rich bright and light lemon that I arrived at. Further experiments showed that this was a great colour to mix with reds and pinks, producing lovely rich earth tones and oranges. I also like to use it in shadows along with blue and purple.
I use this fabulous green a lot now, and always order another tube before I run out of the last, which goes to show how much I like it. I haven't painted many human portraits yet, but when I do, I have a feeling that this colour will be excellent for making skin tones.
My favourite colours to mix with Green Gold so far are: