Call up the que manager select the job and hit delete this will cancel the job. In GSP Plot select the second colour and drag it above the first hit ok, send the job to the edge.
If you reload the vinyl with the bottom of the registration marks sitting level with the top of the right hand side of the bale arm (the bit that holds the vinyl in place) you will have to use your slew keys to get this right, load the second colour.
This is a work around that i have come up with and i must stress that the bottom of the reg mark is just level with the top of the bale arm. You could give this a try but perhaps it might be worth waiting to see if anybody else has any ideas.