using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Windows.Data;
using System.Windows.Media;

namespace WpfApplication1
{
    class ColorConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            int val;
            if (Int32.TryParse(value.ToString(), out val))
            {
                switch (val)
                {
                    case 0:
                        return Brushes.Red;
                    case 1:
                        return Brushes.Green;
                    case 2 :
                        return Brushes.Blue;
                        default:
                        return default(Brushes);
                }
            }

            return default(Brushes);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:Converters="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="284" Width="525">
    <Window.Resources>
        <Converters:ColorConverter x:Key="colorConverter" />
    </Window.Resources>
    <Grid>
        <Label Content="1"  x:Name="testLabel" Background="{Binding RelativeSource={RelativeSource Self},Path=Content,Converter={StaticResource colorConverter}}"/>
        <Button Width="Auto" Height="100" Content="Change label value" Click="Button_Click"/>
    </Grid>
</Window>

private void Button_Click(object sender, RoutedEventArgs e)
        {
            testLabel.Content = new Random().Next(3);
        }