Fix wrong color value (#3247)

Author: mairaw

xml/System.Drawing/Color.xml

@@ -1574,7 +1574,7 @@
         <ReturnType>System.Drawing.Color</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Gets a system-defined color that has an ARGB value of <c>#FF8FBC8F</c>.</summary>
+        <summary>Gets a system-defined color that has an ARGB value of <c>#FF8FBC8B</c>.</summary>
         <value>A <see cref="T:System.Drawing.Color" /> representing a system-defined color.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[