Use Prussian Blue for Dark Backgrounds
Prussian Blue is similar to Winsor Blue, but it is a neutralized semitransparent color. I mix Prussian Blue with Alizarin Crimson and Viridian to create strong darks for backgrounds and to darken other colors.
This dark mixture is almost black, but is still transparent. I use it instead of black tube paints such as Ivory Black, Neutral Tint, Payne’s Gray, etc. which have an undesirable flat appearance.