Colour is noise.
To use or add colour to the pieces is to allow the noise to travel through the work. The desaturation removes the noise, quietness the city, the architecture, the inhabitants, the everyday; it's serenity, it's simplicity, it's meditation.To absorb the pattern in desaturated form is to see the layers, the texture and the meaning; to add colour to the buildings brings in other irrelevant meanings, symbolism of cultures and religions. Of course, white/grey/black have their own meanings too.. in this case they are rendered in the straightforward neutrality of non-colour, of tones rather than pigments.