I experienced the exact same issue with pale colored Ottos from Petsmart about a month or two ago, and yes most of them died. Good thing is they give you your money back within 14 days I believe. I always like to ask when they got the shipment in since a certain percentage of new fish often don't make it long in the store.
I have however bought darker colored Ottos in the past from both Petsmart and my local aquarium stores that were healthy with no issues.
Due to the way the fish are kept, many of them live in stressful conditions so their colors fade. They can control their pigmentation and when they feel safe and well-fed, they will return their darker color.