I tried a different approach of saving the doc as docx and then doing a search and replace in the xml files of document.xml and styles.xml.

In the XML the cyan colours were 00AEFF and E1F4FD.
I changed these to 990099 and FFBDFF respectively

This approach replaced everything except two elements - perhaps because they weren't exactly the same colour.

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Andrew Lockton
Chrysalis Design, Melbourne Australia