fixed linter errors and ambigious variable names

pygrace/colors.py

@@ -1,5 +1,4 @@
 import matplotlib as mpl
-import matplotlib.pyplot as plt
 import numpy as np
 from collections import OrderedDict
 from itertools import cycle
@@ -10,9 +9,9 @@ def make_cmap(colors, mapping=True):
         colors = np.array(colors.values())
     bit_rgb = np.linspace(0, 1, 256)
     position = np.linspace(0, 1, len(colors))
-    _cols = colors[:] + 0 
+    _cols = colors[:] + 0
     for i in range(len(colors)):
-        for j in xrange(3):
+        for j in range(3):
             _cols[i][j] = bit_rgb[colors[i][j]]
     if mapping:
         cdict = {'red': [], 'green':[], 'blue':[]}