How can I add additional admin color schemes into Wordpress 3.8?
I want to add two more with a yellow shade and a green shade.
You can use:
wp_admin_css_color( $key, $name, $url, $colors, $icons );
It's really straightforward, you add a CSS file and your color options.
In WP 3.8, there is a folder called /wp-admin/css/colors
This folder contains the 7 additional (other than default) admin color schemes you can select when editing your user profile.
I'd assume you could copy one of these folders into a new folder, with your own folder name, and then you can edit the CSS contained in the folder.
Upload your new folder to /wp-admin/css/colors and voilà!
Yes, you can have a closer look at the plugin Admin Color Schemes in the repository and at http://wptavern.com/admin-color-schemer-the-easiest-way-to-customize-wordpress-admin-colors