Hello Dr JeffB,
What are you settings for showing external predecessors and successors?
You don't state what version of Project. For 2007 and earlier -- Tools > Options, View tab - Cross Project Linking options.
For Project 2010 File > Options, Advanced - Cross Project linking options.
I've never seen external predecessors as "maroon line item" so I'm guessing you've done some formatting either to Text Styles for External Tasks or for the Bar Styles.
The setting for Cross Project Linking options are project file by file, so it is entirely possible to see different settings for different files.
I hope this helps.
Julie