scatter_matrix `color` vs `c`
I reported the issue below to matplotlib [here](https://github.com/matplotlib/matplotlib/issues/7603#issuecomment-266250371), but they have requested to report it here as it appears (to the matplotlib folks) related to pandas.

The following code gives error, but works replacing `color=` with `c=`

I suspect is either a bug, or some piece of documentation missing?
(matplotlib folks think it is a pandas / scatter_matrix bug - see below)

I'm using:
matplotlib 1.5.3
pandas 0.19.1
python 3.5

This is a sample code:
```
import pandas as pd
import numpy as np
from sklearn.datasets import load_iris
%matplotlib inline

iris = load_iris()
colors = list()
palette = {0: "red", 1: "green", 2: "blue"}

for c in np.nditer(iris.target): colors.append(palette[int(c)])
    # using the palette dictionary, we convert
    # each numeric class into a color string
dataframe = pd.DataFrame(iris.data,
columns=iris.feature_names)
scatterplot = pd.scatter_matrix(dataframe, alpha=0.3,
figsize=(10, 10), diagonal='hist', color=colors, marker='o', grid=True)
```
This is the error trace:
```
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-f3d30057e124> in <module>()
     14 columns=iris.feature_names)
     15 scatterplot = pd.scatter_matrix(dataframe, alpha=0.3,
---> 16 figsize=(10, 10), diagonal='hist', color=colors, marker='o', grid=True)

/Users/e/anaconda/lib/python3.5/site-packages/pandas/tools/plotting.py in scatter_matrix(frame, alpha, figsize, ax, grid, diagonal, marker, density_kwds, hist_kwds, range_padding, **kwds)
    393 
    394                 ax.scatter(df[b][common], df[a][common],
--> 395                            marker=marker, alpha=alpha, **kwds)
    396 
    397                 ax.set_xlim(boundaries_list[j])

/Users/e/anaconda/lib/python3.5/site-packages/matplotlib/__init__.py in inner(ax, *args, **kwargs)
   1817                     warnings.warn(msg % (label_namer, func.__name__),
   1818                                   RuntimeWarning, stacklevel=2)
-> 1819             return func(ax, *args, **kwargs)
   1820         pre_doc = inner.__doc__
   1821         if pre_doc is None:

/Users/e/anaconda/lib/python3.5/site-packages/matplotlib/axes/_axes.py in scatter(self, x, y, s, c, marker, cmap, norm, vmin, vmax, alpha, linewidths, verts, edgecolors, **kwargs)
   3787                 facecolors = co
   3788             if c is not None:
-> 3789                 raise ValueError("Supply a 'c' kwarg or a 'color' kwarg"
   3790                                  " but not both; they differ but"
   3791                                  " their functionalities overlap.")

ValueError: Supply a 'c' kwarg or a 'color' kwarg but not both; they differ but their functionalities overlap.
```
According to @goyodiaz:

> It looks like a pandas issue. pandas.scatter_matrix always pass c to scatter but the caller can optionally pass more keywords arguments, including color. If the caller pass only color then scatter_matrix will pass both c and color and matplotlib will raise with a message that is confusing to the user because they did not pass c. Probably scatter_matrix should either raise with a clearer message or drop the c keyword argument when the user pass color

.
