How to add color search functionality


I'm developing a wallpaper website with wordpress. I would like to add "Color Search Functionality" : user can search images based on color.

I haven't found any WP plugin that could be used for that purpose.

- Do you know any plugin who can do the job ?
- I can develop a plugin but could you give me some advices with the plugin's design (Do I have to use custom fields ? Which action do I have to register ?)

EDIT : I would like an automatic process : when I upload new pictures, a "process" will parse pixels and index colors.