Shading an area between y axis points in a WPF Toolkit Line Chart
<Grid>
    <Grid.Resources>
        <PointCollection x:Key="sampleData1">
            <Point X="0" Y="20"/>
            <Point X="25" Y="30"/>
            <Point X="50" Y="25"/>
        </PointCollection>
        <PointCollection x:Key="sampleData2">
            <Point X="50" Y="25"/>
            <Point X="75" Y="40"/>
            <Point X="100" Y="35"/>
        </PointCollection>
    </Grid.Resources>
    <chartingToolkit:Chart Title="Colored Y Ranges">
        <chartingToolkit:AreaSeries
            Title="First Section"
            ItemsSource="{StaticResource sampleData1}"
            IndependentValuePath="X"
            DependentValuePath="Y">
        </chartingToolkit:AreaSeries>
        <chartingToolkit:AreaSeries
            Title="Second Section"
            ItemsSource="{StaticResource sampleData2}"
            IndependentValuePath="X"
            DependentValuePath="Y">
        </chartingToolkit:AreaSeries>
    </chartingToolkit:Chart>
</Grid>