/usr/share/desktop-base/softwaves-theme/plymouthd.defaults is in desktop-base 9.0.2+deb9u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # Defaults provided by desktop-base for the softwaves theme
[Daemon]
Theme=softwaves
ShowDelay=0
|