this would be pretty useful for sprite recolours, basically, you give it a hue,sat,lum value that you would like too recolor, and then you give it another HSL color that youd like it too recolor too. (rgb could work 2)
then theres extra parameters like hue tolerance, saturation tolerance, and lum tolerance, these values tell the effect to recolor color A's h,s,l, values neighbors (lets say same hue but diff lum or sat colored pixels would be a hue tolerance of 0, and sat/lum tols of 255 ) to the resulting transformation from color A to color B.
bassically the tolerance allows the effect to change the colours which are in the range of the tolerances, these must be HSL to allow for easy recoloring. giving a tolerance of 0 would make the effect only change that resulting parameters (H,S or L) of color A. giving a value of lets say 255 would make the effect change any hue,sat or lum in the resulting parameters hsl.
its hard to explain but i think you get the point. this effect would be usefull for anything pixel art, or with a unified color scheme, but mostly PA.