correct to me.
Each PMW pin goes (through a resistor) to the base of a transistor, all emitter connections go to GND, either power or digital, collector goes to one side of the LED strip, other side of the (each) LED strip connects to 12 volt supply.
LED Strip has a common 12v supply (four wires), wire from other side of LED.
if you connect a meter set to resistance (low ohms), you will see that power GND and digital GND are connected together.
In the time its taken to type describe this it would have been quicker to sketch a diagram and scan it. lol
(I will maybe do that later)