What is a lot more common, however, is that sometimes the insert can feel slightly loose in the tray, and often, especially if you use silver plated trays, you can see the back of the tray next to the glass and it doesn't look very appealing. See here my earlier attempt with one of our brand new oval stickers - can you see the base?
The best way to correct this is very simple - just grab a black permanent marker, and off you go!
Paint the visible edge of the tray:
All the way around:
And paint the edge of the paper, taking care not to go over the sticker or glass:
And there you have it, a lovely finish!