This is an Arduino program for 16 million colors using RGB LED, HC05 Bluetooth module and ATmega328P. The HC05 Bluetooth module is a great module for simple, rapid and cost-effective serial data transfer using the Serial Peripheral Interface protocol to talk to other devices like Arduino, Raspberry Pi, ESP8266 etc., over a Bluetooth connection. It operates at 3.0 volts so it can be powered from the same Arduino board or with a separate 3.3 volt regulator, though the latter option should be avoided if possible as it might introduce a delay of about 1 millisecond when sending data to the HC05 Bluetooth module as this happens via I2C bus.
You can watch tutorials on YouTube – https://www.youtube.com/watch?v=84ax3ZgWGVs
how to use RGB LED – https://www.youtube.com/watch?v=ZBGAOC9nemE