It's complicated :) but I try to explain: On OSX you can use AppKit and related frameworks to create an app or browser like Safari. All colors are subject to Color Management and are converted to your Display profile.

So Safari takes CSS color values assumes they are in sRGB and converts them to your display profile. For Chrome and Firefox this is a different story. They use their own render engine so no conversion takes place here. This is the reason why colors differ between Safari and Chrome/Firefox.

ColorSnapper recognizes if you pick from a Color Managed App and converts the color back to sRGB. There might be a slight difference because of rounding issues, but it's the best you can get.

As for picking from PDFs or Adobe Photoshop: this depends on the app you are using (Preview App, Adobe Reader etc.) and if they have their own Color Management, but that is a little beyond this post. We will soon write a blog post about that on http://colorsnapper.com