Ever wondered if Panasonic ever thought of having a build in shutter matte box like the ones on some Sony models? This practical invention has been around for many years... or is it because of some patent reasons that restricts company from using this practical design? It really sucks to put it out and in again... I know some day I'm gonna loose it somewhere... misplaced it plenty of time.
A bit of electrical tape here and there over the years is an easy fix.
I have a small insert I made inside my lens cap, it's white on one side, and some Pantone chips on the other. I use it to white balance and also get some colour references. Works quite well.