Add custom colors to Wordpress (3.9) TinyMCE color palette

custom_palette.php

function os_overwrite_color_swatch($init) {
	$default_colours = '
	    "000000", "Black",        "993300", "Burnt orange", "333300", "Dark olive",   "003300", "Dark green",   "003366", "Dark azure",   "000080", "Navy Blue",      "333399", "Indigo",       "333333", "Very dark gray", 
	    "800000", "Maroon",       "FF6600", "Orange",       "808000", "Olive",        "008000", "Green",        "008080", "Teal",         "0000FF", "Blue",           "666699", "Grayish blue", "808080", "Gray", 
	    "FF0000", "Red",          "FF9900", "Amber",        "99CC00", "Yellow green", "339966", "Sea green",    "33CCCC", "Turquoise",    "3366FF", "Royal blue",     "800080", "Purple",       "999999", "Medium gray", 
	    "FF00FF", "Magenta",      "FFCC00", "Gold",         "FFFF00", "Yellow",       "00FF00", "Lime",         "00FFFF", "Aqua",         "00CCFF", "Sky blue",       "993366", "Brown",        "C0C0C0", "Silver", 
	    "FF99CC", "Pink",         "FFCC99", "Peach",        "FFFF99", "Light yellow", "CCFFCC", "Pale green",   "CCFFFF", "Pale cyan",    "99CCFF", "Light sky blue", "CC99FF", "Plum",         "FFFFFF", "White"
	';
	$custom_colours = '
	    "911D0E", "OnSite - Dark Red", "D22030", "OnSite - Medium Red", "EA1A2A", "OnSite - Light Red"
	';
	$init['textcolor_map'] = '['.$custom_colours.','.$default_colours.']';
	return $init;
}

add_filter('tiny_mce_before_init', 'os_overwrite_color_swatch');