Back in the day when I was studying at art college I developed a fundness for painting with acrylics and was encouraged to become a colourist. Suffice to say that is were it ended and my working life has been mostly in retail and management to date... I start by gluing any split or ripped parts of the boxes back together and/or (if possible) fill any missing box areas in/up. Next I very carefully clean the boxes up to get rid of dirt and dust. Lastly, (the bit I enjoy) I touch up the worn box areas with acrylic paints, making sure the colours/shades bend with the unworn areas as I go by using a pre-mixed palette. Two years at art college finally of use, albeit only on Transformer boxes. LOL.