Since September 2025 (around the time of a major systemd update) color switching via hooks stopped working.
The same problem occurs with the alternative solution: https://github.com/evanpurkhiser/mkinitcpio-colors using sd-colors.
I have not checked a hook that does not depend on systemd. When I tested changing colors manually via the CLI, the change occurred.
Configuration:
HOOKS="base systemd autodetect microcode modconf kms keyboard sd-setvtrgb sd-vconsole block plymouth lvm2 filesystems"