diff --git a/skimage/_shared/utils.py b/skimage/_shared/utils.py
index e1642102..aad9220d 100644
--- a/skimage/_shared/utils.py
+++ b/skimage/_shared/utils.py
@@ -2,18 +2,7 @@ import warnings
 import functools
 
 
-__all__ = ['deprecated', 'is_str']
-
-
-try:
-    isinstance("", basestring)
-    def is_str(s):
-        """Return True if `s` is a string. Safe for Python 2 and 3."""
-        return isinstance(s, basestring)
-except NameError:
-    def is_str(s):
-        """Return True if `s` is a string. Safe for Python 2 and 3."""
-        return isinstance(s, str)
+__all__ = ['deprecated']
 
 
 class deprecated(object):
diff --git a/skimage/color/colorlabel.py b/skimage/color/colorlabel.py
index f1c91d67..41974f38 100644
--- a/skimage/color/colorlabel.py
+++ b/skimage/color/colorlabel.py
@@ -4,7 +4,7 @@ import itertools
 import numpy as np
 
 from skimage import img_as_float
-from skimage._shared.utils import is_str
+from skimage._shared import six
 from .colorconv import rgb2gray, gray2rgb
 from . import rgb_colors
 
@@ -30,7 +30,7 @@ def _rgb_vector(color):
     color : str or array
         Color name in `color_dict` or RGB float values between [0, 1].
     """
-    if is_str(color):
+    if isinstance(color, six.string_types):
         color = color_dict[color]
     # slice to handle RGBA colors
     return np.array(color[:3]).reshape(1, 3)