Velocikey is a feature that lets you control the speed of lighting effects (like the Rainbow Swirl effect) with the speed of your typing. The faster you type, the faster the lights will go!
For Velocikey to take effect, there are two steps. First, when compiling your keyboard, you'll need to set VELOCIKEY_ENABLE=yes in rules.mk, e.g.:
BOOTMAGIC_ENABLE = no
MOUSEKEY_ENABLE = no
STENO_ENABLE = no
EXTRAKEY_ENABLE = yes
VELOCIKEY_ENABLE = yes
Then, while using your keyboard, you need to also turn it on with the VLK_TOG keycode, which toggles the feature on and off.
The following light effects will all be controlled by Velocikey when it is enabled:
RGB Rainbow Mood
RGB Rainbow Swirl
Support for LED breathing effects is planned but not available yet.
As long as Velocikey is enabled, it will control the speed regardless of any other speed setting that your RGB lights are currently on.
Velocikey doesn't currently support any configuration via keyboard settings. If you want to adjust something like the speed increase or decay rate, you would need to edit velocikey.c and adjust the values there to achieve the kinds of speeds that you like.