So far so good. I was looking for just the basic feature, but I found the multiple-word custom highlight feature even more useful!

I'd like word selection to activate the standard highlighting even when using custom colours (i.e. I select the word -> it highlights all instances with native colour + it shows the custom colours popup)

Custom highlights can be deactivated through the right-click menu. However I think it would be better to have a blank X button next to the other colours.