Fine error line hard to see in preview

My first item I was totally happy with. There was a fine line of white block showing through my colored blocks that was an error on my part, but hard to see on the proof. I wish there had beed a human on that side looking too, it was easily noticeable and preventable. I know it is my responsibility to proof it but I didn't see it until I received my product and went back to look at the proof. Bummer to lose all these cool flyers.