really how old are modern grey cities?

[Igo kyu]

Originally Posted by :FI:Sneaky

This assumes animals can perceive colour (which refers to another thread someplace, and indeed how we perceive it.)

Birds can, some fish see five colours compared to the three that humans do. It's the other mammals, which are often nocturnal when there is little colour to be seen, that are frequently unable to see as many colours as we do.