Shapes in the Diagram control are colored according to the applied theme. To create a custom theme, add a resource dictionary with a Theme element to your application.
Each theme should contain a color palette. To specify a color palette, add the ColorPalette element into the Theme.
To specify how colors are used in a theme, set the Theme.Effects property. This property accepts the EffectCollection object. EffectCollection defines colors shown in the following gallery:
EffectCollection has the following properties:
-ThemeEffects. Specifies colors in the "Theme Styles" group.
-VariantEffects. Specifies colors in the "Variant Styles" group. When a shape is created its default color scheme is taken from this group.
-ConnectorEffects. Specifies connector colors.
To register a custom theme, use the ThemeRegistrator.RegisterThemes method.