Link:
https://docs.python.org/3/library/exceptions.html#exception-hierarchy

Looking at EncodingWarning under exception-hierarchy is displaying BLACK color instead of RED. 

Digging into HTML looks like it is missing the appropriate span class element.

Working:

<span class="o">+--</span> <span class="ne">BytesWarning</span>

Broken:

<span class="o">+--</span> <span class="n">EncodingWarning</span>

See attached screenshot. 

I"m not too familiar with Sphinx but I'm happy to create a PR for this issue if someone could point me in right direction on how to fix this.

That happens because EncodingWarning isn't highlighted as an Exception by Pygments[0]. The doc page gets its exceptions diagram by:
".. literalinclude:: ../../Lib/test/exception_hierarchy.txt"
and all other entries are recognized by Pygments, so we get the "ne" class for them.

A PR for Pygments adding EncodingWarning could be interesting, but I'm not sure the doc build process would pick it up and fix the 3.10 docs issue.

For 3.11, the diagram drawing was changed so no highlighting happens anymore, which fixes the issue for us in the long run.

[0] https://github.com/pygments/pygments/blob/8630e033313647d9579e314f3e8e2882f4558933/pygments/lexers/python.py#L225

Thanks for the information Daniel.