You are wrong. An Mm dog will be merle. An MM dog will be merle. An mm dog will not be merle.Merle is dominant, so a m/m x M/M will produce half M/m (non merle, but carrier) and half m/m (merle)
So it depends if your dog is M/m or m/m .. If your dog doesn't show as merle, its likely M/m.. breeding a M/m to a M/m will produce half m/m.. half M/m.. breeding a M/m to a m/m will produce half m/m and half double merle...
For your dogs genetic makeup, look at the "sires" pedigree. Is there merle in the pedigree? if yes, these two dogs might produce merle.. if no, you'll in up with a litter of tan point dogs who have the possibility to be merle carries (M/m)
I think.. i may be wrong