my tropicanna do the same thing... i live in arizona so i think it might be the sun, then again maybe i don't give them enough water, hum. i don't think that the green ones fade, but i personally like the colored ones. good luck.
kim

An old client gave me a couple of burgundy leaved cannas which I put in full sun on the west side of a house in north central Texas.

They've been struggling for 2 years now.

I've wondered if the dark pigment absorbs heat & stresses the plant.

so this autumn I'm going to move them to a little more congenial area.

I have found that my tropicana does better in shade. But it takes longer for it to bloom. I have a couple other dark leaves that I also put in afternoon shade and the leaves are gorgeous but again this makes them slow to flower.

I guess it is what look you are going for. I grow the cannas for the leaves I am not that impressed with most of the flowers.

Thanks everyone.I grow mostly for the leaves to,I plan to move them to the shade.Debbie