When is a painting finished?

Sometimes it's so easy to know and other times, arg!  At first I thought I would be doing the whole painting in colour but it being primarily black and white seems to fit with memento mori. 






When my husband saw the rose he said it looks like a dead rose. "it is!", I exclaimed with joy. So I'm glad I was able to convey that.  My challenge now seems to be how much more colour do I put