I want to do a half and half of dark purple and black. I know I will need to get as much orange as possible out for a nice purple, but I have no experience with any black semi permanent dyes. Can I leave it orange and cover it? Which black would be best for that?
For a deep pink based purple you won't have to get the orange completely out, such as deep purple by special effects.
I don't think you will have a problem covering orange with any black dye, although you want to avoid cool based blacks to make sure you don't get a murky green fade (unless that's your thing :p) I'm not sure what blacks are warm toned, maybe someone else can chime in there?
I think Directions' black is red-toned - it used to be greenish but I seem to remember it changed a while ago.