As of version 18.3, you can specify the colors and line styles to be used for representing the relationships in your relation maps. Your selection is displayed in the legend in the top right corner of the diagram pane.
To specify colors and line styles
The customized legend helps you identify relation criteria. When working with relation maps, the button is clicked to select by default. If you don't want to see the legend all the time, simply click the button to cancel the selection.