Dark Souls II: The Thread, AND the Game!

[Surrealistik]

I don't think the difference in colouration/hue is just a consequence of the lighting; do they appear the same at the Lordvessel?

Even if it was, the voice is Kaathe's and the relevant parts of the speech are unchanged; i.e. they're both now aligned with the Darklord, regardless of their physical presence.