plotting in pandas is not picking the list of colors passed, it only gets the first value
#### Code Sample, a copy-pastable example if possible

```python
>>> df = pd.DataFrame({"A": range(4), "color": ['red', 'blue', 'blue', 'red']})
>>> ax = df.plot.bar(y='A', color=df['color'])
>>> [p.get_facecolor() for p in ax.patches]
[(1.0, 0.0, 0.0, 1.0),
 (1.0, 0.0, 0.0, 1.0),
 (1.0, 0.0, 0.0, 1.0),
 (1.0, 0.0, 0.0, 1.0)]
```
#### Problem description

It plots correctly but it does not pick the right color per bar. it only pick the color of the first value in the list.
it was working perfectly in pandas 0.19.2

#### Expected Output
 the plot should contain a different color as the list is being passed. Similar to matplotlib behavior and the old pandas version


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

<details> 

pandas: 0.20.2
pytest: None
pip: 9.0.1
setuptools: 36.0.1
Cython: None
numpy: 1.12.1
scipy: 0.19.1
xarray: None
IPython: 5.4.1
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: 2.7.1 (dt dec pq3 ext lo64)
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: None


</details>
