diff --git a/csa/plot.py b/csa/plot.py
index dd2fecc..1f55ae9 100644
--- a/csa/plot.py
+++ b/csa/plot.py
@@ -43,7 +43,7 @@ def show (cset, N0 = 30, N1 = None):
     a = _numpy.zeros ((N0, N1))
     for (i, j) in elementary.cross (range (N0), range (N1)) * cset:
         a[i,j] += 1.0
-    _plt.imshow (a, interpolation='nearest', vmin = 0.0, vmax = 1.0)
+    _plt.imshow(a, interpolation='nearest', vmin=0.0, vmax=1.0, cmap=_plt.cm.gray)
     _plt.show ()
 
 def gplotsel2d (g, cset, source = elementary.N, target = elementary.N, N0 = 900, N1 = None, value = None, range=[], lines = True):