Fix typo in color mapping documentation in quick_start.py

[lubianat]

PR summary

I found this typo while browsing the "Quick start guide." Instead of "a colors," it should read "colors," as far as I can tell.

PR checklist

• [N/A] "closes #0000" is in the body of the PR description to link the related issue
• [N/A] new and changed code is tested
• [N/A ] Plotting related features are demonstrated in an example
• [N/A ] New Features and API Changes are noted with a directive and release note
• [] Documentation complies with general and docstring guidelines

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[tacaswell]

Thanks! I'm 75/25 in favor of this resolution rather than "by a color in colormap", either would probably be OK, but I also like the version in this PR better.

Thank you for you work on this @lubianat and congratulations on your first merged Matplotib PR 🎉

I hope we hear from you again!

[tacaswell]

@meeseeksmachine please backport to 3.9.x

[lubianat]

@tacaswell thanks! Yep, I had the same question myself. I hope I can contribute more in the future, though I am not a super dev like you all :)

[tacaswell]

My first PR was to change a 4 to a 7 #1062

[QuLogic]

@meeseeksdev backport to v3.9.x