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, “Maximum RGB…”
Section 8.38, “Retinex”