I work in printing.
There are currently *NO* commercially available desktop printers that can print white. The only desktop printer that DID print white was the ALPS Microdry printer that used a tape film as the "ink". It has been discontinued for nearly a decade, is extremely problematic to find working units, let alone a supplier for the tape "ink" cartridges.
As for decals, the best quality option and to reduce the delicacy of the final product, only print with a laser printer. Inkjet print decals risk "running" when they get wet. And sealing spray over the print runs two risks. 1) Destroying the print by making it run, 2) making it far too brittle for actual use if you sprayed it too thick.