The current selection of highlight colors in the Mac app is very bad. They are too dark and some colors like the present option for blue make reading the underlying text difficult. In contrast the colors in legacy Papers app were lighter in color and were not shouting in your face. Please consider using softer colors, or better still (if possible) allowing users to select colors.
This is the one thing that has kept me from using Papers. I would like different highlighter colors and thinner pencil/pen options