Adding missing BackgroundColor method

Former-commit-id: 1e35d88182015f11e057a9cc48e0d605db91760a

src/ImageProcessor.UnitTests/ImageFactoryUnitTests.cs

@@ -125,7 +125,7 @@ namespace ImageProcessor.UnitTests
         }
 
         /// <summary>
-        /// Tests that a filter is really applied by checking that the image is modified
+        /// Tests that brightness changes is really applied by checking that the image is modified
         /// </summary>
         [Test]
         public void TestApplyEffectBrightness()
@@ -143,7 +143,25 @@ namespace ImageProcessor.UnitTests
         }
 
         /// <summary>
-        /// Tests that a filter is really applied by checking that the image is modified
+        /// Tests that background color changes are really applied by checking that the image is modified
+        /// </summary>
+        [Test]
+        public void TestApplyEffectBackgroundColor()
+        {
+            foreach (FileInfo file in this.ListInputFiles())
+            {
+                using (ImageFactory imageFactory = new ImageFactory())
+                {
+                    imageFactory.Load(file.FullName);
+                    Image original = (Image)imageFactory.Image.Clone();
+                    imageFactory.BackgroundColor(Color.Yellow);
+                    Assert.AreNotEqual(original, imageFactory.Image);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Tests that a contrast change is really applied by checking that the image is modified
         /// </summary>
         [Test]
         public void TestApplyEffectContrast()
@@ -161,7 +179,7 @@ namespace ImageProcessor.UnitTests
         }
 
         /// <summary>
-        /// Tests that a filter is really applied by checking that the image is modified
+        /// Tests that a saturation change is really applied by checking that the image is modified
         /// </summary>
         [Test]
         public void TestApplyEffectSaturation()
@@ -179,7 +197,7 @@ namespace ImageProcessor.UnitTests
         }
 
         /// <summary>
-        /// Tests that a filter is really applied by checking that the image is modified
+        /// Tests that a tint change is really applied by checking that the image is modified
         /// </summary>
         [Test]
         public void TestApplyEffectTint()
@@ -197,7 +215,7 @@ namespace ImageProcessor.UnitTests
         }
 
         /// <summary>
-        /// Tests that a filter is really applied by checking that the image is modified
+        /// Tests that a vignette change is really applied by checking that the image is modified
         /// </summary>
         [Test]
         public void TestApplyEffectVignette()

src/ImageProcessor/ImageFactory.cs

@@ -332,6 +332,26 @@ namespace ImageProcessor
             return this;
         }
 
+        /// <summary>
+        /// Changes the background color of the current image.
+        /// </summary>
+        /// <param name="color">
+        /// The <see cref="T:System.Drawing.Color"/> to paint the image with.
+        /// </param>
+        /// <returns>
+        /// The current instance of the <see cref="T:ImageProcessor.ImageFactory"/> class.
+        /// </returns>
+        public ImageFactory BackgroundColor(Color color)
+        {
+            if (this.ShouldProcess)
+            {
+                BackgroundColor backgroundColor = new BackgroundColor { DynamicParameter = color };
+                this.CurrentImageFormat.ApplyProcessor(backgroundColor.ProcessImage, this);
+            }
+
+            return this;
+        }
+
         /// <summary>
         /// Constrains the current image, resizing it to fit within the given dimensions whilst keeping its aspect ratio.
         /// </summary>