The second possibility was watercolor pencil. But I've found that some of the colors are much more intense when you apply the water than when they're dry. I'd have to test each color before I applied it. That seemed like too much of a risk as one the water is applied, you're stuck with whatever you've got!
The third choice was watercolor. A down side is that I don't have a lot of experience with it. But up sides are the beautiful, wide array of colors, and the possibility of adding more graphite over the watercolor if I felt I needed to.
The final choice was acrylic washes. I'm very comfortable with acrylic, but I don't use washes on little spaces but over wide areas.
So I chose watercolor and I'm glad I did. I did chose to add a bit of pencil afterward. It was a good choice!