It seems, I think, that there was a short discussion on color dominance on the Yahoo Lilium group in the last year. You might want to try searching the group's site.
http://groups.yahoo.com/group/...
Your hope that two dark pink parents might produce darker pink progeny is not that unusual, and is often true. That the bell curve might shift to the darker end is also a reasonable assumption, but just not always true. It's really a luck of the draw, that the genetics in question will "cooperate" to that end. But the odds, in most cases, are in your favor. Take note that my example of the Midnight strain was meant to exemplify the point with all crosses, not just strains.
Genetics can be extremely confusing. We all learned in school the simple Mendelian concept of dominance and recessiveness, but it is all so
not that simple. Another hypothetical example:
P=dominant pink allele
p=recessive white allele
So the gene combinations are: PP, Pp and pp.
The very basic genetic teaching will say this results in 2 (not 3 or 4) phenotypes (read: visually expressed results):
1) Pink (the PP and Pp genes)
2) white (the pp gene)
For a long time, there was no dissent. But now as knowledge progresses and more factors become known, it's not that straight forward. Even in this simplest hypothetical example, there is now proof that PP is sometimes darker than Pp - we might expect that, but also that Pp is sometimes even darker pink than PP!
Regarding your other questions, I just don't know. Certainly good queries to put to more knowledgeable people, like the Yahoo Lilium group or some of the European Lily groups (at least the ones that converse in English) or the SRGC forum (they have an on going Lilium thread).
Mother Nature is so grand! Life and nature (and flowers) would be so boring without these twists and turns.
