diff --git a/ReactionRecorder.cs b/ReactionRecorder.cs
--- a/ReactionRecorder.cs
+++ b/ReactionRecorder.cs
@@ -313,7 +313,7 @@ namespace DesertPaintLab
 
             bool result = true;
 
-            int solidUpperLeft = testPixelStart + (2 * y * stride) + (2 * x * 3);
+            int solidUpperLeft = testPixelStart + ((y+2) * stride) + ((x+2) * 3);
             int solidLowerLeft = testPixelStart + ((swatchHeight - 4) * stride);
             int solidUpperRight = testPixelStart + ((swatchWidth - 4) * 3);
             int solidLowerRight = solidLowerLeft + ((swatchWidth - 4) * 3);