It’s hard to get a full range of values with Neocolor II watercolor crayons. They all tend to lie in the middle values. This sketch experiments with using Neocolors over waterproof ink to obtain darker values.
Here I’ve dropped out the color so you can see the range of values.
I chose a scene with a wide range of values. The irises were in the shade with bright sunlight behind. I took my glasses off to better see the values. I first used a middle tone gray Faber-Castell brush pen to mark in the mid tone values. Next I added light values with a light gray Faber-Castell brush pen, and then I added black with a Pigma brush pen. Then working left to right I went directly over the grays with various Neocolor crayons. Also, on the right I experimented with brushing over the pen with Neocolor washes. Next I put my glasses back on (to see detail again) and went back over the Neocolor in some areas with mid tone and light gray pen. The ink from the pen melts and blends the crayon color. The light gray pen worked the best for defining shapes with slightly darker values. Finally I used a wet watercolor brush to work over the Neocolor. I did this to strengthen the colors and to drag color into white areas of the paper.
This technique works to increase the number of values of the colors by darkening the existing colors. Both light and dark colors can be made darker. It’s a good, quick way to establish your values first and then add color. However, the neutral gray ink muddies the colors. Next I need to experiment with using complimentary colors to achieve darker values.