I would like to have the option to see phosphorus in green.
Okay, I know this isn't a standard way of coloring phosphorus, but the NCBI uses green and it's nice because it's easier to see the contrast between oxygens and phosphorus in DNA and RNA.
Some of the other Cn3D coloring options would be nice, too. Some examples are: rainbow (colors ROYGBIV from 5' to 3' or amino to carboxyl), charge, temperature, hydrophobicity, and sequence identity (for aligned proteins).