Driving LEDs using and RC receiver
This could be done with a 555 timer, somehow, with a few hundred dollars of testing and man hours and expertise. Maybe. Or you can use any common microcontroller, for a few cents, and a lot less headache. You could use a pic10f, a 6 pin ic that many manufacturers have used to do exactly what you plan. 



Of course, that's a simple RC to ON-OFF type switch. That would be simple for a 555 timer type setup, maybe. But your needs are much more complex. You need to program the PWM reading because you want to adjust the brightness, and then program the output for the ws2812b protocol. It is a smart led, and needs a fairly complex protocol and timings to work.

An arduino would work. A ATtiny would be small and simple. Not many passives needed. Decoupling caps pretty much it.