Did you test if it works if you disable all other addons?
Maybe it's a "multi addon bug" again, like it is very often
I'm asking because I think my chat text anti-fade works with pChat but haven't actually tested this in the past weeks. I only noticed my chat looked like always and I use to have this enabled too.
Edit:
Just tested it again and it's not fading the text for me with the setting in pChat enabled.
Not in zone chat, nor guilds.
After what time does it fade the text for you?