I know a lot of people using photoshop tend to completely neglect color spaces/profiles + refuse to take the time to understand color theory, but this is a pretty short article that does a decent job of explaining why you need to use sRGB for graphics that will be shown on the web.
If you want your work to look consistent in all browers or platforms, you will need to configure photoshop's color settings:
keep in mind that the "save for web" dialog box has a small check box that gives you the option to convert to sRGB (which i believe is checked by default) so make sure it is un-checked once you make these changes.
Not really sure what happens when you convert something that is already sRGB
to sRGB, but I do remember hearing it's not a good idea.