Color squares' interior for pre-moves and last moves.
I proposed this patch upstream but got no response. I'm afraid the project could be dead upstream. So I'd like to propose this here, as nowadays this behavior is present in the online chess websites.
The changes only take effect if line gap is zero, else old behavior is kept (namely only the edges of the squares corresponding to the moves are colored).
I'm using this for a good month and up to now no nasty surprises.
Last move gets "Highlight Color" as specified in View->Board, whereas premove gets "Premove Highlight Color".
Last move example (1. e4):
Premove example (3... c6):