I started with light colors (meaning lots of water than paint) gradually darkening some of the parts (less water or directly from the tube). Then I added the details using pencil, usually I only use darker shades of watercolor or gouache to add the detail, but I decided to try something different and see how it goes.
I like the effect of the pencil. The only challenge I got are the pencil smudge marks, (you know when you draw, the graphite transfers to your hand) to solve this problem I placed paper on top of my artwork so everything will be clean. And that's it. :)