If the attached xref object are dimmed in the drawing you can control the dimming with system variable XDWGFADECTL. The default value is 50.
If you want set xref objects visible, enter XDWGFADECTL on the command line and give the value 0.
The valid XDWGFADECTL system variable value is between -90 and 90. When variable is set to a negative value, the Xref Fading feature is not turned on, but the setting is stored.