I use highlighting in a coded way such that different colors signify importance or categorical differences. The few colors included are great, and more would be so helpful. I achieve different colors by highlight multiple times with the same or different colors, but this has become more difficult with changes made in Zotero version 7 that disallow highlighting over text that has already been highlighted if done in the middle (highlighting over text from the edge works, but I was previously able to highlight words in the middle of a highlighted passage to indicate significance).