A standard "non-silver" CD has a white coat with the CMY (Cyan, Magenta and Yellow) colours applied on top of it.
The CMY colour system used for colour prints is a subtractive model masking colours on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected.
When you enable the "CD Silver" option in your Artwork tab for your CD Release, we don't use CDs with a white coat but instead us CDs with no coat. That means you print CMY directly on the silver body. As a result, all the colours you can print will look duller because you replace anything white or transparent in your design with the silver background from the CD.
This allows you to produce a CD like this:
It only works if your design has larger areas of white; otherwise, everything will look dull and faded. The 3D animation will simulate the effect.