BUG: Scatterplot x-axis label disappears with colorscale when using matplotlib backend
- This issue was reported and resolved in #10611  but returned with 0.24.0.

- I have confirmed this bug exists on the latest version of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
# Your code here
import matplotlib.cm as cm
import pandas as pd
import numpy as np

X = np.random.rand(10,3)

df = pd.DataFrame(X,columns=['t','hlReference', 'STEP_STRENGTH'])

df.plot.scatter(
    x='t', 
    y='hlReference', 
    c='STEP_STRENGTH', 
    cmap=cm.autumn,)

```

#### Problem description

X-axis label disappears when you add a colorscale to a scatterplot when using matplotlib backend.


**UPDATE confirmed this bug occurs in Jupyter and when files are written out**

Example taken from [this SO question](https://stackoverflow.com/a/52632120/4590385) that also shows the two workarounds.

Workaround 1: Get an ax object and pass `ax=ax`.
Workaround 2: Pass `sharex=False`

A previous solution to the problem is discussed in closed issue #10611,  but it appears that stopped working in 0.24.0. 

#### Expected Output

Show the x-axis label.


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

<details>

INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.7.6.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 18.7.0
Version          : Darwin Kernel Version 18.7.0: Thu Jun 18 20:50:10 PDT 2020; root:xnu-4903.278.43~1/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0
numpy            : 1.18.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.2
setuptools       : 49.6.0.post20200814
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.5.1
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.16.1
pandas_datareader: None
bs4              : 4.9.1
bottleneck       : 1.3.2
fsspec           : 0.7.4
fastparquet      : None
gcsfs            : None
matplotlib       : 3.2.2
numexpr          : 2.7.1
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 0.16.0
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.4.1
sqlalchemy       : None
tables           : None
tabulate         : 0.8.7
xarray           : None
xlrd             : None
xlwt             : None
numba            : 0.50.0

</details>
