what color space are the photos in that you are uploading? if they are in Adobe RGB or Prophoto RGB, you might try converting them to sRGB (Edit/Convert to Profile). sRGB is a smaller color space, but it is the standard for internet viewing. from what i understand, if an image is in another color space, the color information may be misinterpreted when it is put on the internet. my advice (and what has worked for me) would be just to convert them into sRGB before uploading. i tend not to see any changes when i convert them, but if you do, at least you can tweak it in PS in advance.