I've the same problem, and it has something to do with how your camera puts the adobe rgb color space on the picture. If you convert you picture in PSE into adobe rgb and save the picture it wil looks good in iphoto.
by what i found out so far it looks like iphoto can't read color space information from the EXIF data so if your camera puts the in formation there the picture looks faded in iphoto (also in preview by the way) You can verify with a script if your pictures have a color profile ( library>scripts>colorprofiles>Show profile info )
I solved this problem so far bij writing a applescript that coverts my pictures automaticly to Adobe rgb in image transfer and i import them after that in iphoto
what camera are you using ? mine is a nikon D70