The shade above the bars is a mask overlay. You can change it by setting custom item style to your bar series definition as follows:
<LinearGradientBrush x:Key="BarMaskBrushOld" EndPoint="1,0.5" StartPoint="0,0.5">
<GradientStop Color="#00FFFFFF"/>
<GradientStop Color="#00FFFFFF" Offset="1"/>
<GradientStop Color="#19FFFFFF" Offset="0.2"/>
<GradientStop Color="#B2FFFFFF" Offset="0.2"/>
</LinearGradientBrush>
<LinearGradientBrush x:Key="BarMaskBrush" EndPoint="1,0.5" StartPoint="0,0.5">
<GradientStop Color="#00FFFFFF" Offset="1"/>
<GradientStop Color="#B2FFFFFF"/>
</LinearGradientBrush>
<Style x:Key="CustomBar" TargetType="telerik:Bar">
<Setter Property="Template" >
<Setter.Value>
<ControlTemplate TargetType="telerik:Bar">
<Canvas Opacity="0" x:Name="PART_MainContainer">
<Rectangle x:Name="PART_DefiningGeometry"
Height="{TemplateBinding ItemActualHeight}"
Width="{TemplateBinding ItemActualWidth}"
Style="{TemplateBinding ItemStyle}" />
<Rectangle Height="{TemplateBinding ItemActualHeight}"
Width="{TemplateBinding ItemActualWidth}"
Fill="{StaticResource BarMaskBrush}"/>
<Rectangle x:Name="PART_SelectedState"
Height="{TemplateBinding ItemActualHeight}"
Width="{TemplateBinding ItemActualWidth}" />
<Canvas.RenderTransform>
<ScaleTransform x:Name="PART_AnimationTransform" ScaleY="0" />
</Canvas.RenderTransform>
<vsm:VisualStateManager.VisualStateGroups>
<vsm:VisualStateGroup x:Name="HoverStates">
<vsm:VisualState x:Name="Normal">
<Storyboard>
<DoubleAnimation To="1.0" Storyboard.TargetName="PART_MainContainer" Storyboard.TargetProperty="Opacity" Duration="0.00:00:00.15" />
</Storyboard>
</vsm:VisualState>
<vsm:VisualState x:Name="Hovered">
<Storyboard>
<DoubleAnimation To="1.0" Storyboard.TargetName="PART_MainContainer" Storyboard.TargetProperty="Opacity" Duration="0.00:00:00.15" />
</Storyboard>
</vsm:VisualState>
<vsm:VisualState x:Name="Hidden">
<Storyboard>
<DoubleAnimation To="0.15" Storyboard.TargetName="PART_MainContainer" Storyboard.TargetProperty="Opacity" Duration="0.00:00:00.15" />
</Storyboard>
</vsm:VisualState>
</vsm:VisualStateGroup>
<vsm:VisualStateGroup x:Name="SelectionStates">
<vsm:VisualState x:Name="Unselected">
</vsm:VisualState>
<vsm:VisualState x:Name="Selected">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_SelectedState" Duration="0.00:00:00.05" Storyboard.TargetProperty="Stroke">
<DiscreteObjectKeyFrame KeyTime="0.00:00:00.0">
<DiscreteObjectKeyFrame.Value>
<SolidColorBrush Color="#B2000000" />
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
<ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_SelectedState" Duration="0.00:00:00.05" Storyboard.TargetProperty="StrokeThickness">
<DiscreteObjectKeyFrame KeyTime="0.00:00:00.0">
<DiscreteObjectKeyFrame.Value>
<system:Double xmlns:system="clr-namespace:System;assembly=mscorlib">2</system:Double>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</vsm:VisualState>
</vsm:VisualStateGroup>
</vsm:VisualStateManager.VisualStateGroups>
</Canvas>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
I hope this helps.