Are you sticking to Macs code or are you writing your own?
If you are sticking to Macs code you have the Fetch function a bit wrong, you should leave function as it was and just fill missing bit.
The Fetch function as in Macs code populates the form displaying for the user, thus you first will run the Fetch function for model to populate the model dropdown box then later run the Fetch function again but this time with the coulour info to populate the colour dropdown. In this case your parementers being passed and received are wrong. (you are trying both model & colour in one run)
Please include your code were you are calling the Fetch function (all the instences were you are calling the Fetch function)
That will be helpfull as to see what your code is trying to do with the Fetch function ie what is being passed and received by the paremeteres.