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The following color filters group contains miscellaneous filters to modify colors in an image, a layer or a selection. You can find some nice effects here.
Section 8.33, “Colorify”
Section 8.34, “Color to Alpha”
Section 8.35, “Filter Pack”
Section 8.36, “Hot”
Section 8.37, “Max RGB”
Section 8.38, “Retinex”