Actually, I'm not sure, but I think you can just change the player color of the CoP and It will change color nicely, if not, figure out the RGB color for vertex, BTW, yellow is #FFFF00. you should know that.
For a nice golden color, check some items in the object editor, some under "miscelaneous" have some golden text (it's a bit dark, but you can always brighten it up). The code for the color in the world editor is "|cTT(transparency)RR(red)GG(green)BB(blue)The text|r".
Yeah, I've decided to use the trigger that changes the circle of power to a player color without changing ownership. Thanks to the person who said Red - 100, Green - 100, that worked too.