Hello everybody!
Since I began making "serious" video job, I decided to use only open-source and Free software for eveything AV (easy under Ubuntu-Studio). And KDEnlive quickly became my favorite (and mostly exclusive) editor.
My first works were mainly shot with a single cam (Canon EOS 60D), whether with forced color t° preset, or left in auto. I never had to wonder about color adjustments (except for esthetic reasons, where I could find the time to experiment a few filters provided and copy/paste the filters to whatever needs it) while editing. The result always looked "coherent".

I recently bought a lesser sensor-sized but much easier to shoot Pentasonic Lumix FZ300 as a main outside cam and inside interviews second cam. And my first "multicam" experiment (with these two cams plus two 550D) was very disappointing.
First, not knowing at all the FZ300, I shot everything in auto color t° mode. While all three Canon where in "cloudy" setting".

The difference between the three Canon ant the Lumix makes it terrible in the editing. I tried to use filters like Color t°'s but never found a way to have matching tints and contrasts. It's even more difficult if I say that we couldn't do a white reference for the cams, and that they were posted so that none of them sees the same lighting (in a little barn with only two small asymetric holes to let the cloudy light in).

[edit] I've tried to shoot with EOS and Lumix at the same preset for color t°, but the color rendering stays very different. So I will have to find a way to compensate permanently this difference.

There's another issue, concerning the "grain" of the picture. The EOSs of these models/generations actually over-sample to 1920x1080 what is a bit lesser (something like 1500 horizontyally have read somewhere) and the caracteristic (and quite esthetic, may I say) "grain" it gives to the image is quite different to the Lumix's fine acutance with no "matter" at all (and, oddly because of the sensors sizes, lesser noise).

Well, I'm juste a beginner and quite ready to learn the next lesson. What are the work methods ? The good and useful filters ? How to use them ?

Thank you in advance for any link, advice, experience return you can provide.

For color grading, maybe look for posts from Inapickle on this forum
You may use the vectorscope to properly tune any color effect you use across cameras.
I really don't practice much, but I believe color curves effect gives you all the freedom you might need.
Saturation is also a parameter that some camera brands boost excessively...