MAIN LINK
Led RGP: http://www.maffucci.it/2014/09/27/arduino-lezione-09-uso-di-led-rgb-parte-1/
Master-Slave: https://www.arduino.cc/en/Tutorial/MasterWriter
Master-Slave between 1 master and more slaves: http://www.logicaprogrammabile.it/comunicazione-tra-arduino-tramite-i2c/
Master-Slave (Master read slave message): https://www.arduino.cc/en/Tutorial/MasterReader
DFPlayer Mini: https://www.dfrobot.com/wiki/index.php/DFPlayer_Mini_SKU:DFR0299