Add greyscale filter.

[melair]

It might be useful to convert to greyscale for clarity. Take the brightness of each pixel and just create an RGB of a shade of white.

From https://stackoverflow.com/questions/14330/rgb-to-monochrome-conversion:
mono = (0.2125 * color.r) + (0.7154 * color.g) + (0.0721 * color.b);

Like brightness it will need to buffer it's original pixels.