500 network question

[bingster]

If you look at a 500 network from the label side, you'll notice that on the back right corner there's probably a spot of paint at the edge of the black plastic top.  I've seen different colored spots on mine (red, yellow, white, etc.).  Does anybody know what these spots of color signify?

[Dennis Markham]

Bingster, I've seen that too.  I have no idea what the color signifies.  Good question.

[benhutcherson]

I've seen it, too, but also don't know what it means.

I wonder if perhaps it's a QC/QA mark, and the color signifies the inspection station. That's my only thought.