If you're a Web designer, expect your CSS colors & your untagged/unmanaged images to look darker on Snow Leopard than on previous versions of the Mac OS. You'll also see less of a visible color shift when going from Photoshop to Flash or other unmanaged environments (e.g. Internet Explorer).
Why is that? Apple has switched to a default gamma of 2.2, which is what Windows has used for years. Colors that aren't color-managed are going to look darker on the whole. Your whole display will now be closer to what Windows users see*.
http://blogs.adobe.com/jnack/2009/09/why_your_web_content_will_look_darker.html
