I actually made it!
In my script file, at the to I define a new variable and copy the $_wp_admin_css_colors
variable into it using the admin_head
hook, since the variable gets destroyed at some later point:
<?php
global $admin_colors; // only needed if colors must be available in classes
add_action('admin_head', function() {
global $_wp_admin_css_colors;
global $admin_colors; // only needed if colors must be available in classes
$admin_colors = $_wp_admin_css_colors;
});
// more script content...
?>