Cause

In the Settings: Connection colors dialog (Options > Settings > Projects > "Project name" > Connections > Connection colors menu option), you can predefine project-specific color codes or color names. The value of the Color / Number property as selected by you is a color code or color name which does not exist in the Connection colors table.

Solution

Possibility 1

Select a color code or color name which is defined in the table of the connection colors.

1. To do this, open the Properties <...> dialog for the connection or connection definition point concerned.
2. Click [...] beside the Color / Number field.
3. Select one of the predefined color codes or names from the Connection colors dialog that opens and click [OK].

Possibility 2

Add the color code or color name that you wish to use to the project-specific connection colors:

1. Select the Options > Settings > Projects > "Project name" > Connections > Connection colors menu option.
2. In the Settings: Connection colors dialog, click (New) and enter the Color code or Color name in the new table row.

Refresh the connections and then start a new check run.