To whom it may concern,
I took a look at your project and believe that I can have it done within 7 days. I think that the best way to get this done would be for me to create a custom font/house style in Sibelius that substitutes the "add note names" function for the color of notehead that you are looking for. Although this wouldn't be a plugin, it would perhaps be even easier, as you could assign a custom keyboard shortcut to the "add note names" function so that any notes you want changed to the color noteheads could simply be highlighted and then changed with the click of a button.
Let me know if this solution appeals to you. I am admittedly not much of a programmer but am an avid Sibelius user and consider it to be one of my specialties. You can see samples of my work on my page if you wish to see the skill of my copyist work.
Thanks for your consideration,
Kyle Scherrer