What causes orange iris blooms to be tan/brownish?

I had some iris that were suppose to be vibrant orange but when they bloomed, the color was almost brown. Similar problem with peach colors. Why can't I get good orange/peach colors? Is there any type of soil amendment that I should use?

I have vibrant orange and they bloom true....lots of peach colored ones too..soil maybe? misnamed?

Were they 'supposed' to be orange or was that just a pic on the package? The big box garden centers are barely 50/50 on correct names/colors/pictures. E-bay is probably closer to 10/90 according to some of the stories.

I believe it is something about the soil. I got some peach iris at the garden center while in bloom. The next year, the color was very disappointing. I'm trying to figure out if there is something with which I can amend the soil and start getting better coloring. Thanks for your suggestions!

Could it have anything to do with how much direct sunlight they get? I have a few that look different when grown in partial shade as opposed to full all day sunlight. But probably not as much difference as you're noting.