Here is some info regarding silk screen & solder masks that seems to be absent from public info. Thought some might be interested and the info might be useful.
Copied From: "AnaLog Services, Inc."
I have been baking unpopulated boards at around 180 or 185C.
Black: No effect on the black soldermask even after several hours. The yellow silk screen ink does darken and become less attractive but is still pretty decent.
Red: Red darkens to a sort of burgundy that is not unattractive. The yellow silk screen ink does the same darkening as on the black, but the reduced contrast of yellow on red results in a much less attractive presentation once it changes. White silk screen ink might be worth trying.
Blue: Blue shifts to greenish blue that is not terrible. The yellow silk screen ink has the same darkening, but looks a bit better on the blue than on the red (subjective).
White: There was some mild yellowing or darkening of the white mask, but it still looks quite nice after many hours of cooking (an attractive off-white). The black silk screen ink did not change at all.
There is some reversion to the original shades on cooling, but I did not watch close enuff to really evaluate that. I *think* I saw that, but I will check closer next time.
One conclusion is that white silk screen ink is the logical choice for all boards *IF* it does not darken too much.
The white and black masks are the only truly opaque masks in what I have seen. It is entirely possible that some of the apparent color change in the red, blue, and green mask is actually the FR-4 darkening and showing through the semi-transparent masks.