USBLED Standalone is a USB LED Linux device driver for stand-alone kernel insertion.
The driver code is exactly the same as the original code written by Greg Kroah-Hartman from its addition into the kernel in 2004.
USB LED driver itself was removed from the kernel in 2016. Hence the need to build and insert USB LED driver as a stand-alone in order to support old USB LED devices (Delcom Visual Signal Indicator, Riso Kagaku LED, Dream Cheeky Webmail Notifier) on the more modern kernel versions.
Ensure kernel headers package is installed:
# On Debian
apt-get install linux-headers
# On Raspberry Pi OS
apt-get install raspberrypi-kernel-headers
Compile the driver:
make build
Insert the driver into the kernel:
sudo make install
After plugging the USB LED device, you'll find the colour files red, green, blue under /sys/bus/usb/drivers/usbled/<id>/ directory.
Each of those colour files has the initial value of 0, indicating the colour is switched off.
Changing the value from 0 to 1 switches the colour on, which should then be visible on the device.