The 72mm #47 Blue Filter from Tiffen is a filter designed to build contrast in black and white photography and creating separation between the tones. For landscape photography the filter will enhance haze and fog, which creates a more dramatic look. Skin tones are lightened for more detail and contrast control. Normally, the filter is intended for B&W photography, but can also be used in color photography to make special effects. The filter has a filter factor of 4.5, so you must increase by 2 1/3 of a stop for your exposure to compensate.
Tiffen filters are not dyed, but are manufactured by using ColorCore technology. This process laminates the filter material between two pieces of optical glass and grinding down and polishing the glass. The glass is finally mounted to the metal ring, which could finally be screwed onto the lens for the desired effect.