Joe C , Nov 17, 2010; 03:18 a.m.
The cause may have to do with the fact that your eyes can see the difference between blue and violet light, but many cameras cannot. Similarly the camera may be able to see the difference between violet and magenta in cases where your eyes cannot.
The car may have been magenta instead of violet, meaning that it reflected red light too, so that the camera may have captured both blue and red. If the dress was violet, then the camera may have captured only blue.
Fixing this would be more difficult, and would probably require making a selection or mask to avoid changing the car and then adjusting the hue of blue in the dress. Here is a quick and dirty version in about a minute, but doing it carefully should not take that much longer.