Shaders: make VertexColor generic attribute.

src/Magnum/Shaders/Generic.h

@@ -66,6 +66,13 @@ template<UnsignedInt dimensions> struct Generic {
      * @ref Vector3, defined only in 3D.
      */
     typedef Attribute<2, Vector3> Normal;
+
+    /**
+     * @brief Vertex color
+     *
+     * @ref Color3.
+     */
+    typedef Attribute<3, Color3> Color;
 };
 #endif
 
@@ -78,6 +85,7 @@ typedef Generic<3> Generic3D;
 #ifndef DOXYGEN_GENERATING_OUTPUT
 struct BaseGeneric {
     typedef Attribute<1, Vector2> TextureCoordinates;
+    typedef Attribute<3, Color3> Color;
 };
 
 template<> struct Generic<2>: BaseGeneric {

src/Magnum/Shaders/VertexColor.h

@@ -93,9 +93,9 @@ template<UnsignedInt dimensions> class MAGNUM_SHADERS_EXPORT VertexColor: public
         /**
          * @brief Vertex color
          *
-         * @ref shaders-generic "Generic attribute", @ref Vector3.
+         * @ref shaders-generic "Generic attribute", @ref Color3.
          */
-        typedef Attribute<3, Color3> Color;
+        typedef typename Generic<dimensions>::Color Color;
 
         explicit VertexColor();