OMG!
I'm so sorry - the editor update for colours that I deployed yesterday evening (my time) broke saving entries.
It's a bit technical but the editor has its own internal data format. I wasn't previously using that format when saving entries because it's not HTML and of course everything here is built around HTML - it's what your browser uses. When loading entries into the editor I convert the HTML that stored in the database into the internal editor format. The editor does most of the heavy lifting on that, but it doesn't convert colours and font sizes...
So I changed the way I save entry data yesterday. I now save HTML which gets displayed directly by your browser (kind of). And I save the editor format in a different table. If the editor format exists, the new system just loads that and doesn't bother trying to parse the HTML. In the long term this means anything the editor can do will be saved into the new format and doesn't need to 'reparsed' when you want to edit an existing entry.
But that requires that one also creates the required new table in the database. Which I did on the test machine and forgot on live...
sigh 😞
Apologies to all those that tried making entries last night. If you can read this entry then I have sorted the problem...