Some say that you can add paint to the primer...I do not know for sure though. Most guys in my area by the color of paint desired and add a flattening agent to it.
Ask you local paint supplier about this, they should know.
pick a primer that is closest to your color. i use to use a black laquer primer years ago made by dupont a dark green would cover good over black.you could also put one or two coats of black laquer on first black paint is less expensivethan a mixed color.