You could try some plants in partial shade to see if leaf color is improved.

The only way to know about adequacy of watering is to dig down at least a few inches to see if the soil is moist. It's doubtful that water availability is significantly affecting leaf color, though.

It's probably time to change out the type of emitter you're using. My favorite is the one below.
It covers a larger area and the flow can be adjusted.

Here is a link that might be useful: spray emitter

Thanks for the responses. Will try these suggestions.

Could it be that they need fertilizer? Cannas are heavy feeders. I'm sure lots of water wouldn't hurt either.

I had this happen with my Tropicanna after I moved and took it with me. I was getting too much direct sun during the heat of the day. The variegated/striated ones just can't take it. I moved it to a more sheltered spot, and the colors of the new leaves were just gorgeous. Of course, it's not growing as fast as it was, but it really looks a lot better.

HW