These packages are maintained by vifino in the vifino/vifino-overlay repository.

eselect repository enable vifino-overlay
emaint sync -r vifino-overlay
emerge app-misc/polychromatic

For packaging or dependency problems, please raise the issue in their repository.

Next up, OpenRazer

Polychromatic is just a frontend. If you haven't already, you'll need to install this driver and daemon: