I think a lot depends on if your friend looks good in green. The thing is that most people who need ASH or COOL hair color need it because they look good in blue colors. If your friend looks awesome in green then maybe the green would work, but then again, most people who look good in green have olive skin and need a neutral color.  They don't necessarily look good in blue. use that as the guideline. The key may be neutral and not gold color. My sister and I are a great example. Both blue-eyed, both fair, both blonde as children. But she can't wear blue and looks great in apple or olive green ( and has neutral highlights) and wears orangey red and I can't wear anything BUT blue and look horrible in green and need a blue-based  cherry red. Anyway, hope that helps.