Bar Plot Does Not Cycle Through Colors
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd

test = pd.DataFrame({'Test':[1,3,5,7,4,5,6,4,7,8]})

colors = [(0.9, 0.9, 0.4),
(0.8, 0.4, 0.6),
(0.2, 0.7, 0.9),
(0.4, 0.4, 0.5),
(1.0, 0.6, 0.4),
(0.3, 0.7, 0.6),
(0.5, 0.5, 0.7),
(0.9, 0.4, 0.4),
(0.5, 0.5, 0.7),
(0.8, 0.8, 0.8)]


test.plot(kind='bar', color=colors)
```
#### Problem description
Bar plot does not use the provided RGB values to color the bar. When I ran: test.T.plot(kind='bar', color=colors), the color is correct, however the unique bars cannot be labeled on the x-axis appropriately.

#### Expected Output
In previous versions, the bar was colored by the equivalent RGB value since there is a 1:1 mapping from bar to RGB.

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.3.final.0
python-bits: 64
OS: Darwin
OS-release: 16.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.20.3
pytest: 3.2.1
pip: 9.0.1
setuptools: 36.5.0.post20170921
Cython: 0.26.1
numpy: 1.13.3
scipy: 0.19.1
xarray: None
IPython: 6.1.0
sphinx: 1.6.3
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.2
feather: None
matplotlib: 2.1.0
openpyxl: 2.4.8
xlrd: 1.1.0
xlwt: 1.2.0
xlsxwriter: 1.0.2
lxml: 4.1.0
bs4: 4.6.0
html5lib: 0.999999999
sqlalchemy: 1.1.13
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: None

</details>
