changing background colour with a converter in xaml : textblock background colour not changing.

Ive bound my data to a textblock which updates with propertychange, and the converter does fire.

    public class Oddsindicator : IMultiValueConverter
        {
           
            public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
            {
                string myPrice = "0";
                string tradePrice = "0";
    
                var colorRed = (System.Windows.Media.Color)System.Windows.Media.ColorConverter.ConvertFromString("#FFB0E0E6");
                var colorWhite = (System.Windows.Media.Color)System.Windows.Media.ColorConverter.ConvertFromString("White");
    
                var unchanged = new SolidColorBrush(colorRed);
                var changed = new SolidColorBrush(colorRed);
    
                if (values[0] != DependencyProperty.UnsetValue)
                {
                    myPrice = values[0].ToString();
                    tradePrice = values[1].ToString();
                }
    
    
                if (myPrice == tradePrice)
    
                    return new SolidColorBrush(colorRed);
                else
                {
                    return new SolidColorBrush(colorRed);
                }
                
    
               
            }
    
           
    
            public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
            {
                throw new NotImplementedException();
            }
        }
    
    
    xaml:
    
    <Window.Resources>
    
        <local:Oddsindicator x:Key="Oddsindicator" >
    
        </local:Oddsindicator>
    
    </Window.Resources>
    
     <TextBlock Text="{Binding BackPrice, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"  TextAlignment="Center" Margin="1"  Grid.Row="4" Grid.Column="2" />
            <TextBlock>
                <TextBlock.Background>
                    <MultiBinding Converter="{StaticResource Oddsindicator}">
                   
                        <Binding Path="BackPrice"/>
                        <Binding Path="Lasttradedprice" />
                           
                    </MultiBinding>
                </TextBlock.background>
            </TextBlock>


Ive used break points at the return and they both fire. My bound value updates perfectly. The converters comparing the values and giving the correct results, just not updating the textblock.
