As you can see on step #1, it's impossible to layer a hard medium over a softer one. The pink colored pencil can only make indentations and scratches over the light blue artist crayon. Here is where the Icarus Drawing Board can help you.

On step #2 the thick layer of crayon is thinned out on the warm zone with a color shaper or a gray paper stump. I use the side, not the point of the paper stump and make small circles until I'm left with a thin, saturated layer of color.

After moving the paper to the cool zone, I'm now able to easily layer colored pencil over artist crayon (see step #3).