If you have my Clay Color System, you already have the clay color recipe for Monaco Blue. It is a pretty close match to my Royal Blue, recipe # 9-4. Here is the color recipe for Dusk Blue using Kato clay:
2 parts Kato Blue
1 part Kato Violet
2 parts Kato Silver
4 parts White Mix # 1-2 *
* See my Clay Color System for this clay base recipe.