Currently Being ModeratedMay 13, 2013 2:04 PM (in response to timruah)
Are these scanned images that were scanned as B/W - grayscale images? If so they will need to be rescanned as color images or have the color profile that's embedded into it stripped or changed to sRGB. This Automator application, Convert to JPG and Embed sRGB profile, which is availalbe from Toad's Cellar will do the job. However you'll have to export the photos out of iPhoto, run the app on the files and reimport into iPhoto.
If there are not grayscale images where did they come from and what color profile do they have (open with Preview and bring up the Info window - Command+i)?