I thought I replied to your question but I dont see it so I will do it again.
Its like fretwork but I save the pieces I cut out instead of throwing them away.
I mark them all so I know what color they need to be then I stick them to a pice of tape on some card stock by what color they need to be. I then spray paint it all.
Once dry I reassemble it all after of course realizing I painted some peices the wrong color which always seems to happen. Once done with that I reassemble it all and glue it to the backer,.