Have a look at the sample application, the file App.xaml contains all the required resources to make it work nicely. Just change the brushes to make it yours.

You must define the Font Family and Font size to use.

• FontFamily AppFont: Defines the font to use in the UI.
• system:Double AppFontSize: Defines the font size to use in the UI.

Example:

<FontFamily x:Key="AppFont">Segoe UI Variable Display,Segoe UI</FontFamily>
<system:Double x:Key="AppFontSize">14</system:Double>

You must define your color theme using specified resource names.

• Color ChromeBorderActiveColor: Defines the color of the window border when it is active.
• Brush AccentColor: Defines the accent color to be used on various UI elements.
• Brush AccentColorDark: Defines the darker accent color to be used on various UI elements (used for hover state for example).
• Brush AccentColorDarker: Defines the even darker accent color to be used on various UI elements (used for pressed state for example).
• Brush IconsAccentColor: Defines the color to be used in Coho.UI bundled isons.
• Brush AccentButtonBorderColor: Defines the brush to be used for border on buttons that use the PrimaryButton style.

Example:

<Color x:Key="ChromeBorderActiveColor">#038387</Color>
<LinearGradientBrush x:Key="AccentButtonBorderColor" StartPoint="0,0.9" EndPoint="0,1">
   <GradientStop Color="#038387" Offset="0" />
   <GradientStop Color="#026163" Offset="1" />
</LinearGradientBrush>

<SolidColorBrush x:Key="AccentColor" Color="#038387" />
<SolidColorBrush x:Key="TitleBarAccentedColor" Color="#038387" />
<SolidColorBrush x:Key="IconsAccentColor" Color="#038387" />
<SolidColorBrush x:Key="AccentColorDark" Color="#026163" />
<SolidColorBrush x:Key="AccentColorDarker" Color="#024D4F" />