Using the photo below, at what point would a patch be considered a "whiteback"? Is there an accepted amount of white or is it a matter of opinion?

 

There is no prescribed amount of cotton/rayon thread that makes a "whiteback" #'s 1 & 2 probably wouldn't be called "whitebacks" 3-6 would.

It's all in the eye of the beholder.

 

A patch with any green thread is universally considered a greenback. However, the same does not hold for the rather new collector term of "white back". It has also been proven (yes, proven, with hard evidence published in the ASMIC quarterly journal) that the amount of white thread on the back can vary widely between patches made on the same production run. The idea that more white means more likely to be WWII is mostly collector myth.

Interesting. Thanks for the replies!