Update label2rgb doc

skimage/color/colorlabel.py

@@ -69,23 +69,29 @@ def label2rgb(label, image=None, colors=None, alpha=0.3,
 
     Parameters
     ----------
-    label : array
+    label : array, shape (M, N)
         Integer array of labels with the same shape as `image`.
-    image : array
+    image : array, shape (M, N, 3), optional
         Image used as underlay for labels. If the input is an RGB image, it's
         converted to grayscale before coloring.
-    colors : list
+    colors : list, optional
         List of colors. If the number of labels exceeds the number of colors,
         then the colors are cycled.
-    alpha : float [0, 1]
+    alpha : float [0, 1], optional
         Opacity of colorized labels. Ignored if image is `None`.
-    bg_label : int
+    bg_label : int, optional
         Label that's treated as the background.
-    bg_color : str or array
+    bg_color : str or array, optional
         Background color. Must be a name in `color_dict` or RGB float values
         between [0, 1].
-    image_alpha : float [0, 1]
+    image_alpha : float [0, 1], optional
         Opacity of the image.
+
+    Returns
+    -------
+    result : array of float, shape (M, N, 3)
+        The result of blending a cycling colormap (`colors`) for each distinct
+        value in `label` with the image, at a certain alpha value.
     """
     if colors is None:
         colors = DEFAULT_COLORS