[LifesGreatestGift]

open file
./clientscript/ckeditor/plugins/colorbutton/plugin.js

On line 257 is where the colors are for the default palette.
It will look like this

CKEDITOR.config.colorButton_colors =
	'000,800000,8B4513,2F4F4F,008080,000080,4B0082,696969,' +
	'B22222,A52A2A,DAA520,006400,40E0D0,0000CD,800080,808080,' +
	'F00,FF8C00,FFD700,008000,0FF,00F,EE82EE,A9A9A9,' +
	'FFA07A,FFA500,FFFF00,00FF00,AFEEEE,ADD8E6,DDA0DD,D3D3D3,' +
	'FFF0F5,FAEBD7,FFFFE0,F0FFF0,F0FFFF,F0F8FF,E6E6FA,FFF';

Each line is a line in the default palette. Just like on the palette, each line contains 8 colors.
So the code and the palette both have 5 rows of 8 colors.

So pick which color you'd like to replace in the palette, say the third color on the second row of the palette, on the second row, third color (colors separated by comma) its DAA520, so replace that with the hex color code you'd like displayed (no # needed).

Upload the modified file, and clear cache