I am not sure where the problem lies. Any suggestions on how how I can isolate and solve the problem?
color management 101: make sure you select the sRGB color space upon export from Lightroom. If you select prophotoRGB (or adobe RGB) your images will look dark and muddy in non-color managed browsers or after uploading to sites that maliciously strip color profiles from images as Picasa does.
Several sites such as smugmug will automatically convert whatever you send
to sRGB. Most simply ignore it however and alas since Internet Explorer
(still >80% browser market share) does not color manage, your colors will
look all wrong. Most other browsers, including FF 3.5,
Safari, and now Chrome
manage so for them it doesn't matter as long as the profile is not stripped
as Picasa does. So if you go to the web or you send files to PC users, you
should simply always use sRGB.
P.S. that advice about adobeRGB is not relevant to Lightroom. Lightroom
always does all of its math in a linear 16-bit prophotoRGB space. This is
far better than using adobeRGB even. In practice you do not have to know
anything about how Lightroom operates behind the scene. Lastly, if you shoot
RAW, you should use
editing even in Photoshop. AdobeRGB is simply not wide enough to capture the
breadth of colors that RAW capture gets you. Lightroom does all this
correctly behind the scenes.