My highlights are 2 light so I applied toner but it lightened my base color which was my natural dk brown hair?

This was about a week ago and I don't know what to do...I want to go a bit darker because the whole thing is too damn light...grrrr!! If I buy a medium brown hairdye at the drugstore, will that turn my highlights green or hide them completely??? I am at loss..I'm going on vacation in a few days so I can't make it to my hairdresser because I have a million things to do....any advice/suggestions?