Colors print washed out - especially yellow/greens

I just got my first magcloud proof and I'm not really happy with the color, which seem really washed out. I wasn't even using very vivid colors in the first place. It's most noticeable in the yellows and greens. In my processing of the photos, the whites have a yellow cast to them to simulate a fading image. In the printed book, those yellow casts turned white. I also had light yellow type and background fill colors that printed as white.

I'm working on a calibrated & profiled monitor. The photos are AdobeRGB and when I soft proof them using U.S. Web Coated (SWOP) v2, they look fine. The PDF file I exported out of indesign looks fine too.

I built the magazine using magcloud's Indesign template. I also followed the guidelines on exporting to PDF found at http://magcloud.com/help/indesign.

So, what's my next step in trying to get the color I expect?

Thanks!