The color key helps you figure out the angle of the light you want in plan view; but not the distance or height of the light. To determine which pipe to hang the light on; the lighting designer must do a “section”. Occasionally a copy of the “center line section” (often just referred to as a section) will be supplied with the theatre base plans – and very rarely by the set designer.

Again: Request a copy of the plans for the theatre you’re going to be working in, and a list of available equipment.

You can also ask if there's a Repertory Lightplot available - many theatres have one which is flexible in its design. Don't just copy it; but you can use it as a guide to see what light sources (inventory) have traditionally been used from what position. Since spaces (and inventories) vary greatly; it can be helpful to visit / explore the space if possible. I recommend standing in your planned acting areas and physically pointing to the various hanging positions; paying particular attention to the angle of your fully extended arm which will serve as a good rough estimate for how resulting shadows will fall on the performers.