Fix a parallelize ReplaceColor

Former-commit-id: becd4521be8fc9d4b15cb2e715acd81a165b81dd
Former-commit-id: d420f50922c6d419e152003d2abdbf9ef12407cc

src/ImageProcessor/Processors/ReplaceColor.cs

@@ -13,6 +13,8 @@ namespace ImageProcessor.Processors
     using System;
     using System.Collections.Generic;
     using System.Drawing;
+    using System.Threading.Tasks;
+
     using ImageProcessor.Common.Exceptions;
     using ImageProcessor.Common.Extensions;
     using ImageProcessor.Imaging;
@@ -72,7 +74,7 @@ namespace ImageProcessor.Processors
                 byte originalB = original.B;
 
                 Color replacement = parameters.Item2;
-                byte replacementR = original.R;
+                byte replacementR = replacement.R;
                 byte replacementG = replacement.G;
                 byte replacementB = replacement.B;
                 byte replacementA = replacement.A;
@@ -85,14 +87,18 @@ namespace ImageProcessor.Processors
 
                 using (FastBitmap fastBitmap = new FastBitmap(newImage))
                 {
-                    for (int y = 0; y < height; y++)
+                    Parallel.For(
+                        0,
+                        height,
+                        y =>
                         {
                             for (int x = 0; x < width; x++)
                             {
                                 // Get the pixel color.
+                                // ReSharper disable once AccessToDisposedClosure
                                 Color currentColor = fastBitmap.GetPixel(x, y);
                                 byte currentR = currentColor.R;
-                            byte currentG = currentColor.B;
+                                byte currentG = currentColor.G;
                                 byte currentB = currentColor.B;
                                 byte currentA = currentColor.A;
 
@@ -112,12 +118,13 @@ namespace ImageProcessor.Processors
                                             // Allow replacement with transparent color.
                                             byte a = currentA != replacementA ? replacementA : currentA;
 
+                                            // ReSharper disable once AccessToDisposedClosure
                                             fastBitmap.SetPixel(x, y, Color.FromArgb(a, r, g, b));
                                         }
                                     }
                                 }
                             }
-                    }
+                        });
                 }
 
                 image.Dispose();