That would change the default colour of all wires. What Marbs is asking for (I believe) is a way to change the colour of the current segment, just as you can in the edit properties form.
There's an existing CCR asking for a SKILL function to do this, CCR 445255 (there are a few duplicate requests).
There is a solution (written by me) which tells you how to remove the colour overrides. You may be able to use this to figure out how they're stored (I'm afraid I don't have time right now to see if I can come up with a workaround):