copy of the default ubuntustudio plymouth theme/script (and .plymouth file edited to reference the '/beforedark/' folder) but pngs replaced to match the Before Dark wallpaper (https://www.opendesktop.org/p/1172924/):
1. download/unzip/copy folder '/beforedark/' into folder /usr/share/plymouth/themes/ (the existing location of default schemes e.g. '/ubuntustudio-logo/') to make them plymouth-accessible. it contains the beforedark.plymouth theme file
2. overwrite the default.plymouth link in /etc/alternatives/ to point to the 'beforedark' theme file: (terminal:) sudo ln -sf /usr/share/plymouth/themes/beforedark/beforedark.plymouth /etc/alternatives/default.plymouth
3. tell the kernel about the change: (terminal:) sudo update-initramfs -u
4. (optional:) change the default desktop wallpaper to Before Dark wallpaper for seamless background transition from boot/splash to login
ubuntustudio logo & wordmark owned by wiki.ubuntu.com/UbuntuStudio/Artwork/UserShowcase. use inkscape with gradients.
matching firefox theme at https://addons.mozilla.org/en-US/firefox/addon/ubuntustudio-before-dark/