You are not the first, it has been claimed to have happened by others (very rarely).

Technically when we have vegetative reproduction we can expect the offspring to be clones of the parent and cannas unlike hydrangeas will not change color based on soil conditions to any noticeable degree. Discounting some radical sort of mutation (very remote) we can usually find a logical explanation; sometimes maybe not.

Are we talking about digging only a few or dividing several dozen plants to transplant? Did you leave any in the original bed? Can we identify the cultivar (name-variety)? Did your cannas produce seed pods with viable seed that fell to the ground? Do you protect your canna bed from freezing? Do you remember seeing rogue plant/plants in the previous years?

As you can see, there are many potential factors that MIGHT explain your situation. It would be very beneficial if we had some good before and after photos of the cannas. As unlikely as you may think, there is likely a simply explanation; we simply may not find it.

Sorry,

Kent