Ashley,

As a general
rule, cannas growing specifically in zone 7 typically need some protection from
freezing in some years. This would apply to any and all colors of cannas
including reds and yellows. In other words the bloom color is not relevant to
being hardy.

If you are simply
asking about the color range of cannas besides reds or yellows I think you will
find a multitude of shades but with some limitations. Our specie cannas
originally used in breeding have only red or yellow blooms for the most part. Progressive
hybridizing has produced many shades of this combination and now includes rose,
salmon, peach, pale yellow, near white, pink etc. Baring mutation, genetic engineering
etc. you will not find blue or violet shades.

Kent