I know what you mean...I bought a LOT of ATBs over the past 15+ years as "solid patternless" and only about 5 were truly patternless when they arrived 
Here's a nice adult female I picked up last year...
>>Those are the nicest I've seen in a long time.I've been out of Amazons for a long time,but 15 years ago that color and pure yellow were always around.Then they sorta dissapeared.Lots of people advertise pure colors but you always see a faint pattern in the backround.But not these.They are REALLY NICE.Godd luck with them.

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Mike Heinrich,
708-428-5616
Mike@amazontreeboa.org
http://www.amazontreeboa.org