By default the highlight color is yellow and that can be manually changed of course, but the change is temporary: in a new document or even after reopening the same document, the default changes to yellow.
The default color is important in that it is the one that can be used to highlight text by selecting text and just clicking that button without using the drop-down menu to select between different colors.
I would like to have that button use a different color that could be then selected with just one click.