make color types public and add stream based tests to prevent future breaking as observed in #52

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

@@ -1,11 +1,21 @@
-namespace UglyToad.PdfPig.Graphics.Colors
+using System;
+using System.Collections.Generic;
+
+namespace UglyToad.PdfPig.Graphics.Colors
 {
     /// <summary>
     /// A color with cyan, magenta, yellow and black (K) components.
     /// </summary>
-    internal class CMYKColor : IColor
+    public class CMYKColor : IColor, IEquatable<CMYKColor>
     {
+        /// <summary>
+        /// CMYK Black value (0, 0, 0, 1).
+        /// </summary>
         public static IColor Black { get; } = new CMYKColor(0, 0, 0, 1);
+
+        /// <summary>
+        /// CMYK White value (all 0).
+        /// </summary>
         public static IColor White { get; } = new CMYKColor(0, 0, 0, 0);
 
         /// <inheritdoc/>
@@ -50,6 +60,43 @@
                 (1 - Y) * (1 - K));
         }
 
+        /// <inheritdoc />
+        public override bool Equals(object obj)
+        {
+            return Equals(obj as CMYKColor);
+        }
+
+        /// <inheritdoc />
+        public bool Equals(CMYKColor other)
+        {
+            return other != null &&
+                   C == other.C &&
+                   M == other.M &&
+                   Y == other.Y &&
+                   K == other.K;
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode()
+        {
+            var hashCode = -492570696;
+            hashCode = hashCode * -1521134295 + C.GetHashCode();
+            hashCode = hashCode * -1521134295 + M.GetHashCode();
+            hashCode = hashCode * -1521134295 + Y.GetHashCode();
+            hashCode = hashCode * -1521134295 + K.GetHashCode();
+            return hashCode;
+        }
+
+        /// <summary>
+        /// Equals.
+        /// </summary>
+        public static bool operator ==(CMYKColor color1, CMYKColor color2) => EqualityComparer<CMYKColor>.Default.Equals(color1, color2);
+
+        /// <summary>
+        /// Not Equals.
+        /// </summary>
+        public static bool operator !=(CMYKColor color1, CMYKColor color2) => !(color1 == color2);
+
         /// <inheritdoc />
         public override string ToString()
         {

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

@@ -1,11 +1,21 @@
-namespace UglyToad.PdfPig.Graphics.Colors
+using System;
+using System.Collections.Generic;
+
+namespace UglyToad.PdfPig.Graphics.Colors
 {
     /// <summary>
     /// A grayscale color with a single gray component.
     /// </summary>
-    internal class GrayColor : IColor
+    public class GrayColor : IColor, IEquatable<GrayColor>
     {
+        /// <summary>
+        /// Gray Black value (0).
+        /// </summary>
         public static GrayColor Black { get; } = new GrayColor(0);
+
+        /// <summary>
+        /// Gray White value (1).
+        /// </summary>
         public static GrayColor White { get; } = new GrayColor(1);
 
         /// <inheritdoc/>
@@ -30,6 +40,32 @@
             return (Gray, Gray, Gray);
         }
 
+        /// <inheritdoc />
+        public override bool Equals(object obj)
+        {
+            return Equals(obj as GrayColor);
+        }
+
+        /// <inheritdoc />
+        public bool Equals(GrayColor other)
+        {
+            return other != null &&
+                   Gray == other.Gray;
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode() => Gray.GetHashCode();
+        
+        /// <summary>
+        /// Equals.
+        /// </summary>
+        public static bool operator ==(GrayColor color1, GrayColor color2) => EqualityComparer<GrayColor>.Default.Equals(color1, color2);
+
+        /// <summary>
+        /// Not Equals.
+        /// </summary>
+        public static bool operator !=(GrayColor color1, GrayColor color2) => !(color1 == color2);
+
         /// <inheritdoc />
         public override string ToString()
         {

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

@@ -6,7 +6,7 @@
     /// <summary>
     /// A color with red, green and blue components.
     /// </summary>
-    internal class RGBColor : IColor, IEquatable<RGBColor>
+    public class RGBColor : IColor, IEquatable<RGBColor>
     {
         /// <summary>
         /// RGB Black value (all 0).
@@ -78,9 +78,15 @@
         /// <inheritdoc />
         public override int GetHashCode() => (R, G, B).GetHashCode();
 
+        /// <summary>
+        /// Equals.
+        /// </summary>
         public static bool operator ==(RGBColor color1, RGBColor color2) =>
             EqualityComparer<RGBColor>.Default.Equals(color1, color2);
 
+        /// <summary>
+        /// Not Equals.
+        /// </summary>
         public static bool operator !=(RGBColor color1, RGBColor color2) => !(color1 == color2);
 
         /// <inheritdoc />