As of version 18.3, you can specify the colors and line styles to be used for representing the relationships in your dependency matrices.
To specify colors and line styles
Open the Dependency Criteria dialog by
double-clicking the Legend.
clicking the button next to Dependency Criteria in the Criteria area.
Open the Style dialog by clicking the button in the Style column of your selected relation criterion.
Change the line color and style to what you like and click OK when you're done.
When you've changed line colors and styles for all the relation criteria you needed to, click OK to close the Dependency Criteria dialog.
Your selection is shown in the customized legend in the top left corner or above of the matrix. The legend is displayed by default in all new projects, but if you don't want to see it all the time, simply click the button in the Dependency Matrix toolbar, then click Legend Location > Do Not Display.