Inclusion of new NAMED_COLORS for MS Excel
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@jfrfonseca : Thanks for this PR!  Quick question: do you know if we test that colors array in our Excel tests?  If not, this might be a good time to write one to make sure we got those colors covered. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=h1) Report
> Merging [#18392](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2952fbd556e1bc4b5fac70c727652b5419e8e096?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18392/graphs/tree.svg?token=eZ4WkYLtcO&height=150&src=pr&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18392      +/-   ##
==========================================
+ Coverage   91.57%   91.57%   +<.01%     
==========================================
  Files         150      150              
  Lines       48702    48702              
==========================================
+ Hits        44597    44599       +2     
+ Misses       4105     4103       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.94% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/excel.py](https://codecov.io/gh/pandas-dev/pandas/pull/18392/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZXhjZWwucHk=) | `97.36% <ø> (+0.65%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=footer). Last update [2952fbd...3b161c5](https://codecov.io/gh/pandas-dev/pandas/pull/18392?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @gfyoung can you push a test for this @jreback : Tests have been added, and all is green.  PTAL. @jreback : Change made, and all is green. PTAL. thanks!