While in comments mode, have a vertical floating dock on the left/right hand side (ideally movable to preferred side) with a line of commenting options and 10 commonly used highlight colours (ideally customisable). This makes switching colours easy while reading in iPad (which is one of its main uses on the iPad).

It saves the user having to click twice to choose a different colour to highlight with.

Additionally, streamline available default colour swatch options with the Adobe acrobat desktop app to make transitions more streamlined.