"Silver" really is a general term for any glaucous appearance on conifers. Colors range from bluish-gray to almost pure white. This color originates in one of two ways:
1. Needles are curled to reveal the stomata on the undersides of the needle which are often a bright silver-white color.
2. Genetic variations cause a lack of chlorophyll in the foliage of some varieties, revealing a translucent, ghostly white color. This usually causes slower growth too which is good for small gardens!