What's the evidence that the colors were added later?

[oshfdk]

So you are proposing a variant of the MRT where what I have been calling original (Rt0) is in fact a restoration of an even earlier and fainter stratum (Rt65535).

Pretending that you were serious: the problem with that theory is explaining why Rt0 failed to restore only and precisely those three stars and two arms. 

This is very easy to explain by adjusting the argument a little. As you said elsewhere, the paint binder can create some kind of protective film that makes it harder for the ink to get to the vellum. Maybe Rt0 did try to restore these lines too, but ended up putting ink on top of the paint where it just flaked off after a while, so by the time of Rt2 neither the original scribe lines nor Rt0 lines were visible.

Seriously, I understand that the MRT is unpleasant because it introduces one unknown variable -- the retracing layer -- for every millimeter of ink trace on the VMS, and thus can explain almost any puzzling detail as a "retracing error".

For me both MRT and the Chinese theories are not very attractive for two reasons:
1) I don't know of any specific evidence that would point towards either of them, so to me they look like conjectures built on very little ground (this is my subjective assessment, of course)
2) If true, neither of them allows for any easy progress in understanding the manuscript. I might entertain a dubious theory that offers some obvious way forward, because you can just take a theory like that for granted and trace it through to the end reading of the manuscript and check if something legible comes out. Both MRT and the Chinese theory basically lead nowhere in practice.