I dyed the underneath of my hair black my hair naturally blonde. I'm scared to dye it because it would still be a different color underneath and it would probably turn orange. I would like to find a way to at least make it fade as much as possible. Any ideas?

The best way to drastically fade hair is bleaching, though you can use things like lemon juice; bleach followed by a toner should give you a nice light blonde with no brass. If you're intimidated by lightening your hair at home, make an appointment with a pro! :)