Customizing the metamodel : Diagrams: Creating and modifying : Creating roadmap-style diagrams : Diagram : Is a Diagram Key provided?
  
Is a Diagram Key provided?
A Diagram Key will be provided, which should indicate the color coding used for Milestones and for Phases.
A key symbol (or collection of symbols) can be placed on the diagram.
There should be an entry in the phase key for each unique phase name and color found on the diagram.
Phase names are determined from milestone names, so if we have milestones a and b then we have a phase a to b.
Phase Color would be affected by Milestone definitions in the same way as specified in the coloring of project phases.