I've changed plymouth-theme-ubuntu-logo to add /lib/plymouth/themes/ubuntu-logo/ubuntu-logo.grub, which is linked to the default.plymouth alternative like this:
I've left derivatives alone, but they can emulate this on their own schedule. Note that Plymouth .script files represent RGB values as decimals between 0 and 1; multiply by 256 and round to get values to pass to the GRUB background_color command.
I've changed plymouth- theme-ubuntu- logo to add /lib/plymouth/ themes/ ubuntu- logo/ubuntu- logo.grub, which is linked to the default.plymouth alternative like this:
I've left derivatives alone, but they can emulate this on their own schedule. Note that Plymouth .script files represent RGB values as decimals between 0 and 1; multiply by 256 and round to get values to pass to the GRUB background_color command.