How do you make Matplotlib is_color_like reject numeric strings before scatter raises an RGBA ValueError?

verbatim agent-facing issue statement

`is_color_like` returning erroneous value on strings of integers
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### Bug report

**Bug summary**

`matplotlib.colors.is_color_like` returns `True` on strings containing integers, even though these are invalid colours when passed to `plt.scatter` or equivalent.

**Code for reproduction**

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```python
import matplotlib
import matplotlib.pyplot as plt
import numpy as np

c = np.arange(1000).astype(str)
X = np.random.normal(0, 1, [1000, 2])

assert all([matplotlib.colors.is_color_like(color) for color in c])
plt.scatter(X[:, 0], X[:, 1], c=c)
```

**Actual outcome**

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```
>>> import matplotlib
>>> import matplotlib.pyplot as plt
>>> import numpy as np
>>>
>>> c = np.arange(1000).astype(str)
>>> X = np.random.normal(0, 1, [1000, 2])
>>>
>>> assert all([matplotlib.colors.is_color_like(color) for color in c])
>>> plt.scatter(X[:, 0], X[:, 1], c=c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/site-packages/matplotlib/pyplot.py", line 2864, in scatter
    is not None else {}), **kwargs)
  File "/usr/lib/python3.7/site-packages/matplotlib/__init__.py", line 1810, in inner
    return func(ax, *args, **kwargs)
  File "/usr/lib/python3.7/site-packages/matplotlib/axes/_axes.py", line 4297, in scatter
    alpha=alpha
  File "/usr/lib/python3.7/site-packages/matplotlib/collections.py", line 899, in __init__
    Collection.__init__(self, **kwargs)
  File "/usr/lib/python3.7/site-packages/matplotlib/collections.py", line 131, in __init__
    self.set_facecolor(facecolors)
  File "/usr/lib/python3.7/site-packages/matplotlib/collections.py", line 685, in set_facecolor
    self._set_facecolor(c)
  File "/usr/lib/python3.7/site-packages/matplotlib/collections.py", line 668, in _set_facecolor
    self._facecolors = mcolors.to_rgba_array(c, self._alpha)
  File "/usr/lib/python3.7/site-packages/matplotlib/colors.py", line 260, in to_rgba_array
    raise ValueError("RGBA values should be within 0-1 range")
ValueError: RGBA values should be within 0-1 range
```

**Expected outcome**

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I would expect either the `scatter` call to successfully recognise these as colours, or the `is_color_like` calls to return `False`. The latter is what I would expect of these two.

**Matplotlib version**
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  * Operating system: Arch Linux
  * Matplotlib version: 3.0.2
  * Matplotlib backend (`print(matplotlib.get_backend())`): Qt5Agg
  * Python version: Python 3.7.1
  * Jupyter version (if applicable): N/A
  * Other libraries: `numpy` 1.15.0

`matplotlib` installed from `pip`. The example code runs without any errors on Windows, Python 3.6, `matplotlib` 2.2.2.
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