DataFrame .plot color attribute works not properly
#### Problem description

color attribute in pd.Series/pd.DataFrame works wrong (not same as color in ax.bar) when I specify a color for each bar

```python
%matplotlib inline
import matplotlib
import matplotlib.pyplot as plt
import pandas as pd
import numpy as np

data = pd.Series([1]*3+[2]*4)
data
```
```
0    1
1    1
2    1
3    2
4    2
5    2
6    2
```
```
colors={1:'b', 2:'g'}
data.map(colors)
```
```
0    b
1    b
2    b
3    g
4    g
5    g
6    g
```
```
data.plot(kind='Bar', color=data.map(colors))
```
![image](https://user-images.githubusercontent.com/9219423/29022109-a61600d2-7b70-11e7-8f47-ae6dd19ea32d.png)
```
_, ax = plt.subplots()
ax.bar(range(len(data)), data, color=data.map(colors))
plt.show()
```
![image](https://user-images.githubusercontent.com/9219423/29022116-ac109f1a-7b70-11e7-8d32-2d6139f941bd.png)

<details>

#### Output of ``pd.show_versions()``

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-81-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.20.3
pytest: None
pip: 9.0.1
setuptools: 20.7.0
Cython: None
numpy: 1.13.1
scipy: 0.19.1
xarray: None
IPython: 6.1.0
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.999999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.9.5
s3fs: None
pandas_gbq: None
pandas_datareader: None
```


</details>
