BackgroundColor is not applied property when DynamicResource is used and button enabling state is changed
<Style TargetType="telerik:RadButton" x:Key="MyTelerikButtonStyle">
<Setter Property="TextColor" Value="{DynamicResource MyPrimaryColor}" />
<Setter Property="BackgroundColor" Value="{DynamicResource MySecondaryColor}" />
<Style.Triggers>
<Trigger TargetType="telerik:RadButton" Property="IsEnabled" Value="false" >
<Setter Property="BackgroundColor" Value="Gray" />
</Trigger>
</Style.Triggers>
</Style>
WORKAROUND:
Use StaticResource:
<Setter Property="TextColor" Value="White" />
<Setter Property="BackgroundColor" Value="Green" />