Assorted questions; crumb color, stiff pre-ferments

I just made Hamelman's "Miche, Pointe-à-Callière" using a mix of whole wheat flour and regular flour. The crumb color came out brown - almost as if I'd added cocoa powder to it, which is weirding me out a little. The whole wheat flour I'm using is a basic supermarket brand (for anyone in the Netherlands - it's AH's "Volkoren tarwemeel"), and the package doesn't say anything about extraction rates or type of wheat or anything like that. I suspect there may be some additives in there that may have provided the color, but on the other hand I can't imagine they wouldn't be listed on the package. I don't know anything about types of wheat - is it possible that it's just a variety that's naturally brown/dark? I've used this flour before and the bread then had a creamy, off-white color, which is what I'd generally expect, but that was in the summer. There's nothing in the Miche formula that could alter crumb color. I'd be kind of annoyed if it turns out this flour has additives and they aren't listed.

Also a question about stiff pre-ferments - Hamelman says they should be "domed" when they're ripe. I'm not really sure how to judge this; I mix it until it's more or less a ball and leave it in a covered bowl to ferment. It has a tendency to flatten out after ~10 hours or so. I mean, I guess the gluten isn't that developed so it doesn't have a lot of support but that seems to be the opposite of "domed". Is it just way over-ripe at this point? Same thing happens with my stiff starter, by the time its next feed comes along it's flattened out. I should note that my breads rise just fine despite that.

Finally, on occasion my bread puffs up a bit like a pita in the oven, i.e. the bottom lifts up from the pan instead of just the top rising. I suspect this happens because the top has crusted too early? I steam with a ramekin of boiling water sitting on the top rack, unfortunately that's the only way I can do it right now I think. I'm not sure how effective that is. EDIT: Never mind, found some info about this issue in the Football loaves thread.

Thanks for any help.