diff -r 2ec323dadca2 Lib/colorsys.py
--- a/Lib/colorsys.py	Sun Aug 04 15:48:29 2013 -0400
+++ b/Lib/colorsys.py	Mon Aug 05 01:16:51 2013 +0300
@@ -33,17 +33,21 @@
 # YIQ: used by composite video signals (linear combinations of RGB)
 # Y: perceived grey level (0.0 == black, 1.0 == white)
 # I, Q: color components
+#
+# There are a great many versions of the constants used in these formulae.
+# The ones in this library uses constants from the FCC version of NTSC.
 
 def rgb_to_yiq(r, g, b):
     y = 0.30*r + 0.59*g + 0.11*b
-    i = 0.60*r - 0.28*g - 0.32*b
-    q = 0.21*r - 0.52*g + 0.31*b
+    i = 0.5990*r - 0.2773*g - 0.3217*b
+    q = 0.2130*r - 0.5251*g + 0.3121*b
     return (y, i, q)
 
 def yiq_to_rgb(y, i, q):
-    r = y + 0.948262*i + 0.624013*q
-    g = y - 0.276066*i - 0.639810*q
-    b = y - 1.105450*i + 1.729860*q
+    r = y + 0.94688221709007*i + 0.62355658198614*q
+    g = y - 0.27478764629898*i - 0.63569107918738*q
+    b = y - 1.108545034642032*i + 1.709006928406467*q
+
     if r < 0.0:
         r = 0.0
     if g < 0.0:
diff -r 2ec323dadca2 Lib/test/test_colorsys.py
--- a/Lib/test/test_colorsys.py	Sun Aug 04 15:48:29 2013 -0400
+++ b/Lib/test/test_colorsys.py	Mon Aug 05 01:16:51 2013 +0300
@@ -69,6 +69,33 @@
             self.assertTripleEqual(hls, colorsys.rgb_to_hls(*rgb))
             self.assertTripleEqual(rgb, colorsys.hls_to_rgb(*hls))
 
+    def test_yiq_roundtrip(self):
+        for r in frange(0.0, 1.0, 0.2):
+            for g in frange(0.0, 1.0, 0.2):
+                for b in frange(0.0, 1.0, 0.2):
+                    rgb = (r, g, b)
+                    self.assertTripleEqual(
+                        rgb,
+                        colorsys.yiq_to_rgb(*colorsys.rgb_to_yiq(*rgb))
+                    )
+
+    def test_yiq_values(self):
+        values = [
+            # rgb, yiq
+            ((0.0, 0.0, 0.0), (0.0, 0.0, 0.0)), # black
+            ((0.0, 0.0, 1.0), (0.11, -0.3217, 0.3121)), # blue
+            ((0.0, 1.0, 0.0), (0.59, -0.2773, -0.5251)), # green
+            ((0.0, 1.0, 1.0), (0.7, -0.599, -0.213)), # cyan
+            ((1.0, 0.0, 0.0), (0.3, 0.599, 0.213)), # red
+            ((1.0, 0.0, 1.0), (0.41, 0.2773, 0.5251)), # purple
+            ((1.0, 1.0, 0.0), (0.89, 0.3217, -0.3121)), # yellow
+            ((1.0, 1.0, 1.0), (1.0, 0.0, 0.0)), # white
+            ((0.5, 0.5, 0.5), (0.5, 0.0, 0.0)), # grey
+        ]
+        for (rgb, yiq) in values:
+            self.assertTripleEqual(yiq, colorsys.rgb_to_yiq(*rgb))
+            self.assertTripleEqual(rgb, colorsys.yiq_to_rgb(*yiq))
+
 def test_main():
     test.support.run_unittest(ColorsysTest)