I have written into the source editor of this page for certain text (the dates) in the Battersea (QB) section to have a background colour. This shows up in Visual mode, but once I click 'save page' the colours disappear. Does anyone know what's wrong?
The issue is you have non-breaking spaces after each of the color names. Replace those with a regular space and it should work.
Actually, they appear to be regular space but the wikitext parser is converting them to non-breaking spaces when generating the HTML. Just get rid of the spaces between the end of the color name and the "|".