[Paul M]

The colours are defined in the javascript files in the "clientscript" folder ;

For vB 3.0.7 you need the vbulletin_editor.js, for 3.5.0 it's vbulletin_textedit.js

In the relevant file named above you will find a section defining the colours in an array ;

var coloroptions = new Array();
coloroptions = {
	"#000000" : "Black",
	"#A0522D" : "Sienna",
	"#556B2F" : "DarkOliveGreen",
	"#006400" : "DarkGreen",
	"#483D8B" : "DarkSlateBlue",
	"#000080" : "Navy",
	"#4B0082" : "Indigo",
	"#2F4F4F" : "DarkSlateGray",
	"#8B0000" : "DarkRed",

The above is just the first few lines.

Edit the colours in this array until your heart is content.