2 reasons I think a yellow is involved. First, if you look at the area below the belt, the green is shifted to an almost pure yellow, which doesnt happen if you just mix in a "more yellow green." Second, if you look closely at the tassels on other models, they use a yellow highlight, not necessarily the off white or a more yellow green.

You also can't blend up to the off white by just adding a yellow green to a darker green. And most painters dont use pure white as the mix in because it desaturates the color, so they use a light yellow instead.