While preparing to run both channels simultaneously (cold+warm), I noticed a very serious design problem.

I wanted to give two independent PWM signals generated by the Atmega328P (Arduino Nano) to the cold and warm channels of the controller. I noticed that the LED board has a common Vcc signal for the warm and cold LEDs. The project originally intended to reduce the number of connection wires, hence the decision to have a common Vcc for the dualLEDs. 

In this case, the common Vcc and the application of two PWM waveforms from two independent Timers will lead to summing on the line. As a result, it will not be possible to control the brightness of the LEDs individually for cold and warm color temperature.

After thinking for a while how I can solve the problem, two solutions came to my mind. The first was to redesign the PCB by splitting the Vcc signal and having it manufactured. While the second solution is to manually disconnect each group of LEDs (cold channel) from Vcc on the PCB and connect with a kynar wire.

The first solution is definitely more elegant, but it requires additional time (PCB manufacturing in the factory) and financial outlay. In the end, I decided to solve the problem by hand using kynar wire and a soldering iron.

This is what the LED PCB looks like after bug fix. The Vcc signal was separated for cold and warm LEDs. The connection wire is hardly visible because the protective insulation is white.