Is there any documentation for addCRamp()/colorize() ?
I didn't include them because they are used in very specific cases and wouldn't be useful for custom nodes.
"addCRamp(y)" adds the Colorizer's color ramp at vertical position "y", and "colorize()" is a hardcoded function which will color the texture at input 0 with the values from the first color ramp. In case a custom node uses this and its layout doesn't match that of the Colorizer (having no inputs or no color ramps), the program might just crash.
Colorizer was meant to be a final node. You can't do much with a colored texture since most filters act upon heightmaps.
You could easily let the user select values for replacement in heightmaps by using parameters, due to the fact that they're grayscale and parameters hold a single value, but it's not possible yet to let the user select a color from their palette as the replacement, because the palette-bound color picker only works coupled with the Colorizer.
Mind explaining what you have in mind, exactly?