I know this is impossible to get achieved flexibly in Sibelius. Probably it’s too late to send this suggestion for the first version of Dorico, but it’s fine if it becomes available in the future releases.
(This could help user focus on notes more efficiently)
Thanks for the suggestion. I’m afraid you are quite right that this will not be included in the first version of Dorico.
It would also come in handy if one needs to write in Gregorian.
You can do it after exporting the file as an image and selecting the layer; at least that is how it worked with Sibelius. I do not think it will be any different with Dorico. But an option of doing it natively would be useful indeed.
I also will eagerly await the ability to have a coloured staff, with the notes the same colour as the staff.
I don’t have any reason to print out like this, but as a writing and arranging tool, it would be very useful.
Maybe this could make the list of things to add to Dorico as soon as possible…
Out of interest, Andy, why would you find being able to colour the staff and the notes to the same colour a useful composing/arranging tool? What would it tell you, and how would you choose to colour them?
For me is much more important, (and probably already done) having coloured notes as in Cubase Score… 
There are DOZENS of alternative approaches. However I addressed “flexibility” in my first post.
I am using LilyPond to fit my such concerns at this moment.
Note that bitmap images always take much more spaces than PDF scores.
This is an issue of visual focus. For me, colored stafflines could help me focus on notes; For Andy, He may want to use colors to help him focus on specific instrument parts.
I generally always start a project with a piano staff, which the final arrangement is based on. This piano line will not be part of the final score, so it would be good to have this staff stand out, especially if the actual arrangement does contain a piano line as well - keeping the working piano part looking different would be helpful, and I would think having the notes the same colour as the staff would also help.
To set the colour need only be part of the staff setup, it doesn’t need to change throughout the piece.