Colors are set limited by a javascript library. Having said that, the number of colors (styles / layers) can easily expand to how many styles you feel is necessary. This sample has 24 additional styles. The colors on the picture has been quantized using this library within the Node Editor:
these examples would be portrait fotos of family members, friends or collegues,
so I think you can take any copyright free image from Wikipedea etc, like a polititian,
movie actor etc.
Vector graphics work well with the pointillism routine on this node. Pictures do not work as well at this moment.
Circle packing is one of the item being investigated for this node. The stipple generator is a favorite to work on as well.