A good tip for signing a document is to sign it in blue ink. If you sign in black it is difficult to tell which is the original and which is the photocopy. I would never recommend signing a document in red ink.
I prefer it if my boss uses blue ink to make revisions to a document. I find I can notice the changes better than with black ink. I don't like revisions done in red ink as I can't see red very well, but that is a personal choice for me, others may prefer it.
I had one boss who would make revisions in pencil. I think I started needing glasses after working for him. I would not recommend using pencil.
How can the assistant influence their boss to use a colour of pen that is easier on the eyes? I only provide my boss with blue pens. Problem solved!