Randomize Color Scheme Selection in Theme

on my site I'm using cenetric, a child theme of genesis and this theme comes with some predefined color schemes.

//* Add support for additional color style options
add_theme_support( 'genesis-style-selector', array(
    'centric-pro-charcoal' => __( 'Centric Charcoal', 'centric' ),
    'centric-pro-green'    => __( 'Centric Green', 'centric' ),
    'centric-pro-orange'   => __( 'Centric Orange', 'centric' ),
    'centric-pro-purple'   => __( 'Centric Purple', 'centric' ),
    'centric-pro-red'      => __( 'Centric Red', 'centric' ),
    'centric-pro-yellow'   => __( 'Centric Yellow', 'centric' ),
) );

Now I am looking for a way to create a random color scheme, so that every time any user visit my site, the color scheme gets automatically selected. I've tried the following:

$thm_out = array("Charcoal", "Green", "Orange", "Purple", "Red", "Yellow");

//* Add support for additional color style options
add_theme_support( 'genesis-style-selector', array(
    'centric-pro-charcoal' => __( 'Centric Charcoal', 'centric' ),
    'centric-pro-green'    => __( 'Centric Green', 'centric' ),
    'centric-pro-orange'   => __( 'Centric Orange', 'centric' ),
    'centric-pro-purple'   => __( 'Centric Purple', 'centric' ),
    'centric-pro-red'      => __( 'Centric Red', 'centric' ),
    'centric-pro-yellow'   => __( 'Centric Yellow', 'centric' ),
    'centric-pro-random'   => __( 'Centric '.$thm_out[array_rand($thm_out, 2)].'', 'centric' ),
) );

But its giving the following error in my admin panel and also not working properly.

Warning: Illegal offset type in C:\xampp\htdocs\dev\wp-content\themes\centric-pro\functions.php on line 69

So, can you guys please help me to fix this issue?