My highlighter color in Pages on my iPad Mini used to be yellow. Then some months ago, it changed so that for new documents, the highlight color is violet, which is too dark for me. Fortunately, I still have older documents with the yellow highlight color. So, I make a copy of one of these documents and then select and delete all the text inside the copied document ("Select All" then backspace). Though all the text is gone, the document 'remembers' the original highlight color, yellow. When I then use that document for my new content, the highlights are in yellow, not violet. Magic!