This was working! Now it is not.

However, I just changed the colour script to a newer one, and it works, again.

The deprecated HTML would be <font color="red"> … but it's been recommended not to use that for years now.

The current "right" way to do color is with <span style="color: red"> - which most browsers will automatically convert the above into.

The Quest text-processor code that generates that is {colour:red:text goes here}.

I won't use it again but it did actually seem to work - until it didn't.

And I found it in the tutorials. Of course, I had gone there looking for it specifically,
or rather the span style script, which I took it for,
and didn't read the part above it and below it, that said which engines it could or could not be used with.
It was here -
https://docs.textadventures.co.uk/quest/tutorial/text_formatting.html
"This text is the current foreground colour, but ."

I have switched over to the Quest text processor code, and everything is working well, now.
I guess I will just have to be more careful copying text without reading.