When a bulb has a frosted covering, it will affect the color of the bulb but not the color index.  A light bulb’s color rendering index, or CRI, is referred to its brightness, but a frosted bulb will only affect its appearance.  A clear bulb will always be the sharpest light, but a frosted or milky bulb can still have a high lumen output. It will simply affect the overall look of a bulb to have the light appear dull or “milky.” For a complete lighting reference check out our blog here