I just discovered an interesting filter that I've started to play with: Singh-Ray Gold-N-Blue It is a polarizing filter that influences the blue or gold colors in an image. Here are some snapshots showing its effects. All images shot on a tripod @ 24mm on an FF body with some slight cropping to remove vignetting. Otherwise, no adjustments were made in PP. All images shot as RAW. No filter. Standard circular polarizer. Because of the relatively wide angle of view there is a darker band in the sky in the middle of the image (the effect of the polarizer filter) which trails off towards either edge. This is more pronounced on the left, because I wasn't shooting at exactly 90 degrees relative to the sun. Gold-N-Blue filter rotated to maximize the gold effect. Not very complementary for this particular image. Just like with the standard circular polarizer, the effect is more pronounced in the center because of the wide angle of view. Gold-N-Blue filter rotated to maximize the blue effect. Again, other than a slight crop nothing was done to these images in PP. No masking. No layers. No gradients. Nada. All differences between the images relate to the different filters and not to changes in camera settings. Because these are polarizing filters, the effects will obviously vary with light source and angle relative to the light source.