Symbolic icons are increasingly preferred in sytem tray, at least in KDE, which is a better and safer choice for smart color theme - icons turning black or white according to changing backgrounds with the use of transparency in the panel containing the system tray.
I have created such a set for my KDE panel, which made a big difference. The actual status symbols like check mark can also have different colors to cater also for different use cases.
I justed wanted to share this here in case Insync developers might like to take this account in future releases or at least other KDE users can make use of it from here: https://drive.google.com/file/d/1kj8hBtkz2M25bf5Kk0u299Bi0FPgroEj/view?usp=sharing
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Hi, the latest version (3.4.0.40973) includes a new set of status icons.
In case the Linux team intended also to resolve this issue, I’m sorry to report that nothing changed in this respect.
If there was no such intention, no problem - I’ve resolved this issue on my end anyway. 
In the scenario mentioned in my original post, all (shades of) colors are automatically converted to either black or white, because all status icons have to monochrome (no shades of grey either).
(1) The waves in those icons are too close to one another - if the team would like to cater for such a scenario as well, they need to be like the icon at the top left corner of this webpage (there lines look even better).
(2) When monochromized, there is no difference between normal and offline, and the all colored emblems (alert, paused, synced, syncing) are displayed as a solid circle merged with the waves - as seen in the top 2 examples in my original post.
If the team would like to cater for such a scenario as well, (a) there should also be an emblem for offline (e.g. a red X cross cutting into the left half of the waves) and the emblems should be without that those colored background circles but those colors should be used directly for the (currently white) emblems, and they should be smaller and with a good distance from the wave lines.
These icons are the result of my amateur work to resolve this issue in my system:
Thanks a bunch for reaching out again, @Sadi! I will forward this once more to our Linux team and get their insight on your feedback about the Insync icon 