For the record, that's exactly the response you get when there is no ADC at the expected address (I2C: 0x4D). Which suggests tool and h/w don't match. What does i2cdetect -y 0 produce?
root@Omega-67F5:~# i2cdetect -y 0
The RGB LED on the Expansion Dock consists of three LEDs that give you the ability to create RGB colors on the Expansion Dock.
GPIO 17 controls the red LED. GPIO 16 controls the green LED. GPIO 15 controls the blue LED.
The RGB LED is active-low, meaning that setting the GPIO to 0 will turn on the designated LED.
So in the next commands n must be 17, 16 or 15
gpioctl dirout n
turn OFF the R, G or B LED
gpioctl dirout-high n
fast-gpio set n 1
turn ON the R, G or B LED
gpioctl dirout-low n
fast-gpio set n 0