Exactly what do the green and red blocks of text indicate?

Your Help explains how to see who changed what section, but once I click into one of those history entries, I see green and red blocks of text.

I was assuming that green meant text that was added and red meant text that was removed (or altered), but I've seen a couple of things that make me wonder if that's actually so.

Could you please augment your help so that it covers all the way down to the individual history entries?