use single instances of black and white for rgb/gray colors

src/UglyToad.PdfPig.Tests/Graphics/TestOperationContext.cs

@@ -28,7 +28,7 @@
         public TestOperationContext()
         {
             StateStack.Push(new CurrentGraphicsState());
-            CurrentPath = new PdfPath(CurrentTransformationMatrix);
+            CurrentPath = new PdfPath();
             ColorSpaceContext = new ColorSpaceContext(GetCurrentState);
         }
 

src/UglyToad.PdfPig/Graphics/ColorSpaceContext.cs

@@ -76,13 +76,37 @@
         public void SetStrokingColorGray(decimal gray)
         {
             CurrentStrokingColorSpace = ColorSpace.DeviceGray;
-            currentStateFunc().CurrentStrokingColor = new GrayColor(gray);
+
+            if (gray == 0)
+            {
+                currentStateFunc().CurrentStrokingColor = GrayColor.Black;
+            }
+            else if (gray == 1)
+            {
+                currentStateFunc().CurrentStrokingColor = GrayColor.White;
+            }
+            else
+            {
+                currentStateFunc().CurrentStrokingColor = new GrayColor(gray);
+            }
         }
 
         public void SetStrokingColorRgb(decimal r, decimal g, decimal b)
         {
             CurrentStrokingColorSpace = ColorSpace.DeviceRGB;
-            currentStateFunc().CurrentStrokingColor = new RGBColor(r, g, b);
+
+            if (r == 0 && g == 0 && b == 0)
+            {
+                currentStateFunc().CurrentStrokingColor = RGBColor.Black;
+            }
+            else if (r == 1 && g == 1 && b == 1)
+            {
+                currentStateFunc().CurrentStrokingColor = RGBColor.White;
+            }
+            else
+            {
+                currentStateFunc().CurrentStrokingColor = new RGBColor(r, g, b);
+            }
         }
 
         public void SetStrokingColorCmyk(decimal c, decimal m, decimal y, decimal k)
@@ -94,13 +118,37 @@
         public void SetNonStrokingColorGray(decimal gray)
         {
             CurrentNonStrokingColorSpace = ColorSpace.DeviceGray;
-            currentStateFunc().CurrentNonStrokingColor = new GrayColor(gray);
+
+            if (gray == 0)
+            {
+                currentStateFunc().CurrentNonStrokingColor = GrayColor.Black;
+            }
+            else if (gray == 1)
+            {
+                currentStateFunc().CurrentNonStrokingColor = GrayColor.White;
+            }
+            else
+            {
+                currentStateFunc().CurrentNonStrokingColor = new GrayColor(gray);
+            }
         }
 
         public void SetNonStrokingColorRgb(decimal r, decimal g, decimal b)
         {
             CurrentNonStrokingColorSpace = ColorSpace.DeviceRGB;
-            currentStateFunc().CurrentNonStrokingColor = new RGBColor(r, g, b);
+
+            if (r == 0 && g == 0 && b == 0)
+            {
+                currentStateFunc().CurrentNonStrokingColor = RGBColor.Black;
+            }
+            else if (r == 1 && g == 1 && b == 1)
+            {
+                currentStateFunc().CurrentNonStrokingColor = RGBColor.White;
+            }
+            else
+            {
+                currentStateFunc().CurrentNonStrokingColor = new RGBColor(r, g, b);
+            }
         }
 
         public void SetNonStrokingColorCmyk(decimal c, decimal m, decimal y, decimal k)

src/UglyToad.PdfPig/Graphics/Colors/RGBColor.cs

@@ -1,34 +1,47 @@
 namespace UglyToad.PdfPig.Graphics.Colors
 {
+    using System;
+    using System.Collections.Generic;
+
     /// <summary>
     /// A color with red, green and blue components.
     /// </summary>
-    internal class RGBColor : IColor
+    internal class RGBColor : IColor, IEquatable<RGBColor>
     {
+        /// <summary>
+        /// RGB Black value (all 0).
+        /// </summary>
         public static RGBColor Black = new RGBColor(0, 0, 0);
+
+        /// <summary>
+        /// RGB White value (all 1).
+        /// </summary>
         public static RGBColor White = new RGBColor(1, 1, 1);
 
         /// <inheritdoc/>
         public ColorSpace ColorSpace { get; } = ColorSpace.DeviceRGB;
 
         /// <summary>
-        /// The red value.
+        /// The red value between 0 and 1.
         /// </summary>
         public decimal R { get; }
 
         /// <summary>
-        /// The green value.
+        /// The green value between 0 and 1.
         /// </summary>
         public decimal G { get; }
 
         /// <summary>
-        /// The blue value.
+        /// The blue value between 0 and 1.
         /// </summary>
         public decimal B { get; }
 
         /// <summary>
         /// Create a new <see cref="RGBColor"/>.
         /// </summary>
+        /// <param name="r">The red value between 0 and 1.</param>
+        /// <param name="g">The green value between 0 and 1.</param>
+        /// <param name="b">The blue value between 0 and 1.</param>
         public RGBColor(decimal r, decimal g, decimal b)
         {
             R = r;
@@ -37,11 +50,39 @@
         }
 
         /// <inheritdoc/>
-        public (decimal r, decimal g, decimal b) ToRGBValues()
+        public (decimal r, decimal g, decimal b) ToRGBValues() => (R, G, B);
+
+        /// <inheritdoc />
+        public override bool Equals(object obj)
         {
-            return (R, G, B);
+            if (obj is RGBColor color)
+            {
+                return Equals(color);
+            }
+
+            return false;
         }
 
+        /// <inheritdoc />
+        /// <summary>
+        /// Whether 2 RGB colors are equal across all channels.
+        /// </summary>
+        public bool Equals(RGBColor other)
+        {
+            return other != null &&
+                   R == other.R &&
+                   G == other.G &&
+                   B == other.B;
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode() => (R, G, B).GetHashCode();
+
+        public static bool operator ==(RGBColor color1, RGBColor color2) =>
+            EqualityComparer<RGBColor>.Default.Equals(color1, color2);
+
+        public static bool operator !=(RGBColor color1, RGBColor color2) => !(color1 == color2);
+
         /// <inheritdoc />
         public override string ToString()
         {