Underglow LEDs can provide a nice lighting effect. You can go either of two ways about it: use surface mount RGB LEDs, or use a WS2812b compatible LED strip. The surface mount LEDs provide a more even lighting effect, while the LED strip may be slightly easier to install. The kit provides five extra LEDs so you’ll have room for error.
Surface mount LEDs
Surface mounts LEDs are temperature sensitive. Try to apply heat for at most four to five seconds at a time. Alternate between LEDs to reduce the risk of damaging an LED. The data sheet advices a maximum temperature of 250 degrees Celcius (around 480 degrees Fahrenheit).
The surface mount LEDs are to be installed on the bottom side of the PCB, on the footprints marked RGB1 to RGB10. You’ll notice each footprint has a corner cut out with a dot next to it. The cutout and dot should match the cut out corner of the LEDs.
To start, apply a tiny blob of soldering tin to one of the four pads for each of the RGB footprints.
After having soldered one pad, take a single RGB LED with your tweezers and align the marked corner of the LED with the marked corner on the PCB. The PCB also has a dot near the angled corner so you’ll be able to verify the alignment after soldering the LED.
Taking the LED with tweezers in one hand and your soldering iron in the other, place the LED near the pad and form a joint between the pad and the LED with your soldering iron. If you’re not happy with the alignment, heat up the pad again and shift the LED around using the tweezers.
Then, after you're happy with the alignment, solder the other three pads.
If you use a LED strip, you can make use of the row of pads along the top of the PCB next to the microcontroller area. The pads to use are RGB, VCC and GND.
The LED strip will also have three pads marked in the same way. Using a piece of copper wire, form a connection between each pair of RGB, VCC and GND.