So hi everyone, the redoubtable tpf member and bonanza seller has an album of what appears to be comparison of cobalt blue v royal blue nano pictures. I'm not sure of which nano is which colour ... perhaps other can shed some light ... but here is a link to the album of this very informative seller. I hope seller doesnt mind me posting it as I found it very interesting:
https://plus.google.com/photos/107863734128221945235/albums/5759198458894912849
https://plus.google.com/photos/107863734128221945235/albums/5759198458894912849