Custom DependencyProperty

CODE :

public class baseComboBoxItem : ComboBoxItem
    {
        public static DependencyProperty IsAllowHighlightProperty = DependencyProperty.Register("IsAllowHighlight", typeof(bool), typeof(baseComboBoxItem), new PropertyMetadata(true));  //the "true" is for custom default value, because the type is "bool"
        public baseComboBoxItem()
        {
         
        }

        public bool IsAllowHighlight
        {
            get
            {
                return (bool)base.GetValue(IsAllowHighlightProperty);
            }
            set
            {
                base.SetValue(IsAllowHighlightProperty, value);
            }
        }
    }

So, we can use IsAllowHighlight in XAML

<BC:baseComboBox x:Class="MakeMoney.BaseControls.comboColorPicker"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:BC="clr-namespace:MakeMoney.BaseControls"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300"
             Width="100" Height="26" SelectionChanged="baseComboBox_SelectionChanged">  
    <BC:baseComboBoxItem Background="#FF000000" IsAllowHighlight="False"><TextBlock Text="" /></BC:baseComboBoxItem>
    <BC:baseComboBoxItem Background="#FFCCCCCC"><TextBlock Text="" /></BC:baseComboBoxItem>
    <BC:baseComboBoxItem Background="#FFDDDDDD"><TextBlock Text="" /></BC:baseComboBoxItem>
</BC:baseComboBox>

And also, for template triggers

<ControlTemplate.Triggers>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="IsHighlighted" Value="True"/>
                                <Condition Property="IsAllowHighlight" Value="True" />
                            </MultiTrigger.Conditions>
                            <Setter Property="Background" TargetName="Bd" Value="{StaticResource baseHighlightedBackground}"/>
                        </MultiTrigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>