If you're shooting raw, it's a combination of the camera sensor, lens and - most importantly - the .dcp or .icc profile used by your raw development software that's resulting in the colours you like so much. If you're shooting straight-out-of-camera JPEGs, it's the camera's JPEG engine. The K-1 and any lens can produce exactly the same colours as the Z7 and any other lens by creating a suitable profile (a one-off and not-too-difficult task) and applying it during raw development.
Choice of lens - subject to availability on any chosen platform - is responsible for how sharp, aberration-free, flare-resistant and "characterful" the reendering will be. More than any other aspect, it's arguably the available glass that can make or break a system for each photographer individually, if image "quality" - again, a subjective thing - really matters to them... BUT, what one person values or prioritises in a lens, another may not, and vice versa. "Better" is subjective; at least with most modern lenses, since they all perform reasonably well.
So... colour rendering and performance of lenses are largely independent of the camera. Both the K-1 and Z7 should perform equally well here, if profiling is carried out and lenses are chosen wisely (both of which are entirely within the photographer's control).
What we're left with, then, is the AF performance and viewfinders of mirrorless and DSLR systems respectively, which is at the core of the ongoing mirrorless vs DSLR debate... a debate that can never be won in favour of either, since each offers certain benefits and downsides, and folks will always have differing use-cases and prefereneces (I shoot both, preferring each for different use-cases... but I far prefer an optical viewfinder when the situation allows).
That said, it's great you've found a system that works better
for you. Enjoy the Z7... it's undoubtedly a fine camera, and you've picked some fine glass to go with it
And, if you decide to hang on to the K-1 in the long run, look into creating profiles that give you the colours produced by the Z7 and Voigtländer lenses. That way, you'll have both systems capable of the same colour rendering, a choice of the lenses you like on each system, and the option to choose EVF or OVF as your use-case and/or mood dictate