I've noticed that if you live in a cold climate and you're not out in the sun much in the winter, the bags take a really long time for the trim to darken. I have three new LV's with the light leather and they are not changing very quickly because I live in NH - trust me on this - the snow reflection does nothing to darken the bags!!
One of the 3 bags was changing nicely (my Hudson) but I had to have it replaced, so now I have a brand new one with the super light leather, so I have to start from scratch. I'm going somewhere sunny next week, but only bringing one bag, so at least I get to decide which one I want to bring and darken up.
I'm not really complaining because I could have much worse problems, but I know what you mean about the patina. Once there's a patina, there's less worrying about water stains too.