Every time I highlight some words in a doc in LibreOffice, unless it is a standard yellow or blue, the color changes when I close the .doc and then reopen it. Why? Is there a way of preventing this from happening? Thank you
To what file “format” did you save?
If it not was LibO Writer’s native format (extension .odt or .fodt), try again with that one. Alien formats may cause problems, and may even be “hostile” in a sense.
Hello, thank you for your prompt answer. Yes, you’re right, I was working with a .docx, in .odt that problem is solved. Thanks. But if I want to share this doc in a .docx format (i.e. with people I work with but are not using libreoffice), then there is no solution but to use only standard colors (like yellow), is there?
Cheers
@arl1972: put the blame on their side 
Word claims to be able to read .odt, so then send them an .odt. Depending on what collaboration is required from them, this could be enough. But BEWARE, if they edit the document and send it back to you, you’ll face a similar issue: Word will convert to a format alien to it. Conversions will take place, probably more severe than those on your side because Word format has less expressiveness than ODF.
The safest workflow could be to work and save in .odt on your side. Send a copy in .docx. When receiving back a revised document, open it separately. Open your original .odt in its own window. Scroll both side by side and retype the differences in your .odt. Don’t copy/paste as this will import all Word manual formatting (Word does not know about character styles amongst others). You can ease the task by enabling Track changes in the copy you make in .docx format.
When you click the drop down to select your highlight colour, select the drop down list within the dialog to select the palette compatibility to get the full range of colours that docx can use.