Unfortunately, yeah. I'm not 100% positive on all of this, so don't quote me, but I think there are three primary areas that affect costs: Paper, Ink, and Art.
Printing in color is just more expensive than B&W, in general, due to more inks involved, and it's a bit more complicated because you have to make certain the colors are printing correctly (Anyone who's ever done any printing in color knows that sometimes what is on your screen isn't quite what comes out on paper).
I think the paper stock is different as well. They use a slightly heavier, more expensive paper to hold the colors properly.
Finally, color art is more expensive than B&W art. This is one (of several) reasons why Missions got bumped up in cost a couple bucks.
All of that adds up. And a $20 B&W product ends up being $30 or $40 instead.