Looks as if some wishes have been granted and Kontakt 5.6.6 now offers a return to coloured keys as well as a few other improvements. Hopefully, this will address some of the previous complaints.
"The KONTAKT team have released the latest free update: Version 5.6.6 is now available for download in Native Access.
This update brings a much-requested return to full key coloring on the virtual keyboard, making switch placements and sound and sample type positions clearer. It also fixes some rare but troublesome bugs.
To update, just start your Native Access app and open ‘Available updates’."