I'm seeing code text with a variety of colors. Two recent examples:
In this image taken from the first one, there's text in light blue, dark blue, and red.
And poking about, the light blue has "span class" typ, the dark blue is kwd and the dark red is lit. Other text is pln.
Is this a Winter Bash thing or is it the way code text will appear for the foreseeable future?
What you are seeing there is syntax highlighting. This can be formatted explicitly in a post, for example, you can turn on Bash syntax highlighting for a code snippet by adding a tag before it:
<!-- language: lang-bash -->
Syntax highlighting is also applied automatically according to a post's tags. In this case, the question has the tag python3, so all code in the question and all of its answers will be displayed with Python 3 syntax highlighting.
This is often not what you want... for example the question relates to Python but is mainly about package management and contains a code-formatted block of APT output. You can turn off syntax highlighting with a tag like this:
<!-- language: lang-none -->
or to turn off all syntax highlighting in a post
<!-- language-all: lang-none -->
For more information see What is syntax highlighting and how does it work? | MSE.
<!-- language: -->.