I wonder if soaking fig cuttings in colloidal silver or using as a foliar spray on fig leaves would kill FMV, it is supposed to kill bacteria,pathogens and viruses.

Boy, I don't know about using heavy metals on cuttings. Luckily with the advent of antibacterial soaps and other safer anti pathogenic products, we don't have the need to go that route. I know the Romans would put their silver coins in their milk to keep it from spoiling, but with plants' keen ability to uptake heavy metals, I wouldn't want you to end up like "the blue guy". Remember him?

Or maybe it will cause the fig to mutate and turn blue,just think of the possibilities, Blue Madeira,LSU blue,Malta blue and so on.

Now that would be cool...blue Madiera. Sounds like a mixed drink!

Grant, I've wondered the same thing. I plan to spray a couple of my FMV loaded fig plants with a 10ppm solution this Spring, to see how they do. ( Grise de St. Jean, especially ) It cannot hurt them. Silver is a necessary element, and you'll find it in most good multi-mineral and vitamins. There was a reason they made babies teething rings and silverware from silver. Bacteria and germs cannot live in contact with it. Hospitals are using it in everything from counter tops to catheters. It's in almost all of your athletic clothing, to kill bacteria (BO). The guy who turned blue consumed huge quantities of bad quality colloidal silver. Myself, and many of my friends have used it for years, to ward off colds and flus, with no side effects. Used properly, high quality colloidal silver is a safe alternative chemical fungicides and antibacterial products. 

I've tried lots, including copper fungicide, neem oil. The best way to avoid fungus is to not let your temps get too high(over about 75). Even with decreased air flow you can still avoid mold and fungus. Use coco coir which allows about 30% airflow even when fully saturated. Yes, higher temps will facilitate faster routing but you are risking more fungus. I only wash my cuttings in very hot water briefly now,works perfectly.

I've used colloidal silver to fend off fungus on my cuttings.  Worked pretty well.  Reapplication was needed until the furry fungus was visibly gone.  Worth a try for fmv treatment.