ESP8266 Community Forum

Ok, I see. It's ok that the one driving its colour gets warm, but as mentioned shouldn't get burning hot.
One more thing I have in mind is that your separate grounds may cause this somehow. Unfortunately I'm too less skilled with in-deep electronics to point this out. But I would definitely not use it this way.

TIP122 is a standard darlington transistor, so roughly has a voltage drop of ~1V, depending on the number of LEDs and PWM frequency you get non neglegible powerloss on the transistor that may be too much for dissipation without heatsink.
Go for real FET like mentioned here viewtopic.php?p=71919#p71919 and make sure you also have all necessary modifications in the sketch...

Thanks schufti for joining in with this hint!

As far as I researched, the mentioned IRLZ44N MOSFET can even replace the TIP122 without changes to the layout:

Base - Gate -> to pin 5, 6, 7
Collector - Drain -> to R, G, B (strip)
Emitter - Signal -> to GND

Could someone please confirm this to be correct?