My dad has red-green colorblindness, meaning that blue is the only color he can see. I recently went on a trip to North Carolina with him and he kept mentioning how beautiful all the blue flowers that grew there were. We're building a cabin in Park Rapids, MN, which is in zone 3a, and for my Dad's birthday I would like to plant him a garden of blue flowers. What flowers would you reccomend to grow there? Most of our land is under full shade, although a partial sun area would be possible too.