I have green hair

My hair does the same thing. Mostly in my very processed ends. It's a buildup of color. Since I applyed so much blonde to it, when I applied the dark blonde it turned it green at the ends. I left mine cause my top layer is almost a white blonde and under it's dark. It doesn't come out. You'll have to lift  the color out. Use  something other then Feria, that product is so hard on hair! Oopsie hey?
It's hard to go darker from Blonde. Blonde is a tricky color cause in order to go darker you pretty much HAVE TO GO DARK. Like a brown or something. Good luck.

http://www.styles101.com/haircolor2.html it has the hair color wheel and tells you how to correct the green. hope it helps.