raster
When raster-color is active, specifies the combination of source RGB channels used to compute the raster value. Computed using the equation mix.r - src.r + mix.g - src.g + mix.b - src.b + mix.a. The first three components specify the mix of source red, green, and blue channels, respectively. The fourth component serves as a constant offset and is -not- multipled by source alpha. Source alpha is instead carried through and applied as opacity to the colorized result. Default value corresponds to RGB luminosity. Default value: 0.2126,0.7152,0.0722,0.