Custom Post Type Icons Theme from Settings

I am working on a real estate listing system for a large organisation, and I am trying to work out how to let users choose which ‘colour scheme’ they want for the Admin back-end.
At the moment, I’m looking to just let users change the icon colours for the custom post types.
For examples, I have a Listing custom post type, with a specific icon (icon_listing.png), which at the moment is just house icon in black. But if the system administrator suddenly needs to change the icons to blue (e.g. company rebranding), I want them to be able to go into a Settings page (custom made, not the usual WP one), and choose ‘Blue’ for the Admin colour scheme.
I have some colour variations of each file – icon_black_listing.png, icon_blue_listing.png and so on, and the icons are set on the Plugin PHP file in the usual way:
'menu_icon' => plugins_url( 'img/icon_black_listing.png', __FILE__ ),
Is there a way to have a call that extracts the administrators option, and drops it in there? E.g.:
'menu_icon' => plugins_url( 'img/icon_[COLOURSCHEME]_listing.png', __FILE__ ),

It may seem unnecessary, but I like to give users a lot of flexibility in how their system looks on the back-end, and I intend to build this functionality into all of my future plugins.

Thanks for any pointers of help that you guys/gals can give 🙂