how to have several highlight colours in a .docx document

I have previously been using a number of different highlight colours in a text document to differentiate questions that need to be addressed by different people who will receive the document. Up until recently this has been working well. Then recently once I save the document in a different format (i.e not .odt but .docx so that all the people receiving the document can read it on their various software) all the highlighted parts of text all become bright yellow. Not even a mellow yellow, a very bright and very bold YELLOW. I think this problem may have started for me after the last installation of a new version towards the end of February (5.0). How can I go back to my colour coded way of working, and keep the colours even when the document is saved as a .docx ?