Added some color table tests

tests/Tests/SKColorTableTest.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Runtime.InteropServices;
 using NUnit.Framework;
 
@@ -27,6 +28,16 @@ namespace SkiaSharp.Tests
 			(SKPMColor)SKColors.Blue
 		};
 
+		[Test]
+		public void CreateIndex8Bitmap()
+		{
+			var info = new SKImageInfo(320, 240, SKColorType.Index8, SKAlphaType.Opaque);
+			var ct = new SKColorTable(Colors);
+			var bitmap = new SKBitmap(info, ct);
+			Assert.IsNotNull(bitmap);
+			Assert.AreEqual(ct, bitmap.ColorTable);
+		}
+
 		[Test]
 		public void MembersRetrieveSingleColorWithAlpha()
 		{
@@ -134,5 +145,30 @@ namespace SkiaSharp.Tests
 			}
 			Assert.AreEqual((SKColor)0x7EA4C639, bitmap.GetPixel(182, 348));
 		}
+
+		[Test]
+		public void Index8ImageCanChangeColorTable()
+		{
+			var path = Path.Combine(PathToImages, "index8.png");
+
+			var codec = SKCodec.Create(new SKFileStream(path));
+			var info = new SKImageInfo(codec.Info.Width, codec.Info.Height, SKColorType.Index8, SKAlphaType.Premul);
+			var bitmap = SKBitmap.Decode(codec, info);
+
+			var colorTable = bitmap.ColorTable;
+			Assert.AreEqual((SKColor)0xFFA4C639, colorTable.GetUnPreMultipliedColor(255));
+
+			var invertedColors = colorTable.Colors.Select(c =>
+			{
+				var c2 = (SKColor)c;
+				var inv = new SKColor((byte)(255 - c2.Red), (byte)(255 - c2.Green), (byte)(255 - c2.Blue), c2.Alpha);
+				return (SKPMColor)inv;
+			}).ToArray();
+
+			colorTable = new SKColorTable(invertedColors);
+			bitmap.SetColorTable(colorTable);
+
+			Assert.AreEqual((SKColor)0xFF5B39C6, colorTable.GetUnPreMultipliedColor(255));
+		}
 	}
 }