If I recall correctly the painting is called "Fleur de Sud" which means "flower of the south". He said that during the rain of Beast Butler in New Orleans that the ladies of the city came up with the idea of arranging flowers in such a way as those who knew about the practice would see an image of the flag while those unaware of the practice would not notice it. I don't remember which flag he said was being displayed.
He told me there was a painting of one of these floral arrangments and that prints of the painting could be bought from the gift shop at Confederate Memorial Hall in New Orleans.
I'll look and around and see if Google shows anything. Again, I'm running on the memory of a long ago casual conversation so take this info for what is.