I really don't understand the finer points of colour setting. However, I just watched Guardians of the Galaxy on UHD blu-ray on simple Cinema/warm 1 with no adjustments and the images were vibrant and otherworldly beautiful.I have the 40" model. I do use True Cinema mode but have found the 'Normal' colour gamut to be inaccurate for SD/HD content. I checked it with an i1Display Pro and green/red are both undersaturated causing the image to appear quite washed out. The peak red hue is too much toward yellow, causing reds to appear orange. It's worth testing this with a 100% red source so see if your model exhibits the same issue. I noticed it first with the Red Dead Redemption logo on the PS4.
One quick fix is to change the HDMI Content Type to 'Photos', but this only works for HDMI sources. Alternatively you can change the gamut to native, which will actually over-saturate the colours but does fix the issues with the red hue. I also increased the backlight to around 40 (subject to room lighting conditions).
In the end I re-calibrated the HD true-cinema mode, starting with the Native gamut to get the colours more accurate, it now looks pretty good.
Although the grey scale tracking was good in true cinema, gamma was inaccurate (2.4 tracks closer to 2.1) as well as the colour issues mentioned. Again, I had to make gamma adjustments to get closer to 2.4.
I was surprised with the poor HD colour tracking as this is an area that Panasonic are usually quite good at out of the box. I'd previously had a 43" Samsung R7400 (returned due to IPS panel) and a Hisense B7500 (returned due to ghosting issues), however both of these had better colour accuracy in their equivalent 'cinema' modes.
UHD/HDR is much more accurate though and the wider colour gamut seems pretty accurate out of the box in True Cinema mode. I haven't bothered making any adjustments other than using 2.4 gamut to lower some of the black levels.