Here is a plugin that gives your WordPress admin pages a whole new look. Apply lets you change admin logo, menus, login page, footer, and other settings without touching any code. You can change global / menu colors, hide parts from the admin bar, and sort your menus via drag & drop.
Apply also lets you import/export your data. Want to customize the color, logo, or images on your login page? No problem. Flatfull is the developer behind this paid plugin.