This appears not to be Tiger specific, but occurs with iPhoto 5 on Panther as well. This is a bad enough bug that one should not update to iPhoto 5 until it's fixed. From Macintouch:
Regarding the iPhoto/ColorSync Profile post from the Apple discussion boards, here is an interesting experiment to show the relationship between different color profiles:
Open "ColorSync Utility" from /Applications/Utilities. Click on the Calculator icon in the main window. Select two different profiles for the right and left sides (sRGB Profile on the right and Generic RGB Profile on the left, for example) and then move any slider. Note the opposite slider(s) and how far they move in comparison in order to achieve the same color in the other profile.
For example, if Generic RGB Profile has red set to .5 and green and blue set to 0, sRGB Profile has red set to .5732, green to .0975 and blue to -.0339. You can see immediately the relationship between various profiles and how if values are saved from one profile and "applied" to another profile (not using ColorSync functionality but just "saved" as belonging to the other profile) how the colors would be very different.
James Bailey is on the right track in pointing to a change in embedded profile as being the reason for color shifts in edited iPhoto files. But ColorSync is not the problem: ColorSync is just OSX's color management system.
It seems that iPhoto is not properly re-saving the embedded profile of an edited file, turning it into an 'untagged' file (without color management information). When a color-managed application such as Photoshop or iPhoto opens what it sees as an untagged file, it will assign whatever default RGB profile it happens to be using, thus displaying shifted color. The color information is all present and correct, it's just that the wrong profile is being used.