As I remember PWM is to control the brightness of the LED. LEDs can only shine at one brightness, they're either on or off, so to dim them to half-brightness you need to have them on half the time, off half the time. That's how you get all the different colours from three LEDs.

But they can switch on and off very fast, so if 50Hz is flickery, you can use 500Hz, or 5000Hz. Most microcontrollers have circuitry for this built in, so you just literally write a different constant into the controller.

I once made an LED dashboard for use in police cars. After it was rolled out, it was discovered that the flicker frequency was interfering with the radio (the only bug ever found in my code!)

My client called me back in to fix it, so I added a zero in the relevant place, and recompiled the code.

£400 for about twenty minutes work.