diff --git a/tutorials/colors/colormaps.py b/tutorials/colors/colormaps.py
index 6d3b58b6a8c6..cf4f63097ea1 100644
--- a/tutorials/colors/colormaps.py
+++ b/tutorials/colors/colormaps.py
@@ -391,4 +391,4 @@ def plot_color_gradients(cmap_category, cmap_list):
 # .. [bw] http://www.tannerhelland.com/3643/grayscale-image-algorithm-vb6/
 # .. [colorblindness] http://www.color-blindness.com/
 # .. [vischeck] http://www.vischeck.com/vischeck/
-# .. [IBM] http://www.research.ibm.com/people/l/lloydt/color/color.HTM
+# .. [IBM] https://ieeexplore.ieee.org/document/480803/