The Tiffen 2 x 3" 2 Tropic Blue Soft-Edge Graduated Filter helps to specifically add a cool, greenish-blue coloration to skies and other bright areas of an image while allowing a portion of the image to remain neutrally colored. The filter's coloring is densest at the edge and tapers to clear by the middle, with a soft-edged transition between the density and clear areas. The 2 color density provides less tropic blue coloration than the 3 density, but more than the 1 density filter.