Spatial Filter Effects work with the X and Y location of pixels more than directly with Color 1 or Color 2.
Some Spatial Filter Effects are extremely useful. Specifically, the Airbrush Effect changes your current brush into a gradient Airbrush. The Stipple Effect changes your brush into a stipple brush. Also the RGBA Discard, Selective Discard, RGBA Replace, and Selective Replace Effects are very important for getting rid of unwanted colors as you paint.
The following gives a brief list of each Spatial Filter Effect, and what it does. Click the name for a detailed page outlining that Effects capabilities:
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