diff --git a/skimage/color/delta_e.py b/skimage/color/delta_e.py
index 3703254e..9f8cd2e8 100644
--- a/skimage/color/delta_e.py
+++ b/skimage/color/delta_e.py
@@ -60,6 +60,7 @@ def deltaE_cie76(lab1, lab2):
     References
     ----------
     http://en.wikipedia.org/wiki/Color_difference
+    A. R. Robertson, "The CIE 1976 color-difference formulae," Color Res. Appl. 2, 7-11 (1977).
     """
     l1, a1, b1 = _unpack_last(lab1)
     l2, a2, b2 = _unpack_last(lab2)
@@ -165,6 +166,7 @@ def deltaE_ciede2000(lab1, lab2, kL=1, kC=1, kH=1):
     ----------
     http://en.wikipedia.org/wiki/Color_difference
     http://www.ece.rochester.edu/~gsharma/ciede2000/ciede2000noteCRNA.pdf (doi:10.1364/AO.33.008069)
+    M. Melgosa, J. Quesada, and E. Hita, "Uniformity of some recent color metrics tested with an accurate color-difference tolerance dataset," Appl. Opt. 33, 8069-8077 (1994).
     """
     L1, a1, b1 = _unpack_last(lab1)
     L2, a2, b2 = _unpack_last(lab2)
@@ -275,6 +277,7 @@ def deltaE_cmc(lab1, lab2, kL=1, kC=1):
     ----------
     http://en.wikipedia.org/wiki/Color_difference
     http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE94.html
+    F. J. J. Clarke, R. McDonald, and B. Rigg, "Modification to the JPC79 colour-difference formula," J. Soc. Dyers Colour. 100, 128-132 (1984).
     """
     l1, a1, b1 = _unpack_last(lab1)
     l2, a2, b2 = _unpack_last(lab2)