If you want to essentially do get HTML/CSS equivalent of
This is red text
in reStructuredText using Sphinx, you can do this by creating a role:
.. role:: red
Then you use it like this:
:red:`This is red text`
There should be only one tick mark ` at the end of the line above.
You, of course, have to have
.red { color: red }
in your CSS file.