Color Settings: The Edit>Color Settings option allows you to change the way your computer views your photo files. You can choose between having no color management, always optimizing the color for computer screens, always optimize for printing, or allow me to choose.
No color management - will ignore and discard color embedded profiles if any exist.
Always optimize for computer screen - This setting is set for sRGB mode and will keep all colors within that range as they exist. This ensures an accurate display of your photos for any computer that accepts sRGB color modes.
Always optimize for printing - This setting sets your photos within the AdobeRGB range which is commonly used when you print images.
Allow me to choose - This mode will always assume that your photo should be in sRGB mode, but will also give you the option to change to AdobeRGB if a color profile is not present.