2. I want to get a hexadecimal value as my output instead of the RGB values. I have tried changing "DEC" to "HEX" in all "Serial.print" commands but that didn't work. I also tried incorporating a separate decimal to hex conversion function but even that didn't work.
"That didn't work" has to be just about the lamest statement anyone could possibly make. The code, wherever YOUR code is, does something. You want it to do something. All we know is that those two somethings are not the same thing. No clue what either something is, though.
I don't suppose that it is important how the device is connected to the Arduino.