How to get rid of plum/red hair shade? HELP?

I've got this old hair dye in my hair its not a bright red, its got dark dark red/plummish tones to it and I want to get rid of it, I've heard that an "orange based" hair dye insted of "green based" which is more directed at red hair, will work better, but I have no idea what is an orange based hair dye, can anyone give me any examples?? what is an orange based hair dye? I know that green based will be ashy but what about orange based?