Drummer_kidder
I'll point out that in the fourth ED of Brotherhood, "Shunkan Sentimental", the various homunculi are shown with at least one or both eyes glowing red. And during various scenes, such as when Bradley attacks Lan Fan in episode 22, his right eye (the one not covered by the eyepatch) glows red.
Since Pride operates in and from the shadows, I wondered it sometimes the red eyes are meant to be Pride watching, but the characters don't see it. After all, Al's "eye lights" aren't meant to actually be there, it's just something given for us in the audience. Movies and tv shows do this a lot, like sinister music playing to warn us in the horror films.
I could be wrong, but it's just an idea I had.
I like this theory, it best explains why there would be scenes with random red glowing eyes... I doubt we'll ever know for sure, though. Some things are best left a mystery.
Completely random note, I had to write a captcha for this post and it says "I think so"... it fits pretty well I think.
xd