I am late to the party! I like to think of white collars along the line of what people consider pinstripes in crested geckos, you have a full pin stripe, and a partial pinstripe. With white collars I would consider:
What would you all consider this chahoua? I'm leaning towards white collar, but it does have some broken spaces.
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Take this animal for example. It clearly has a white collar, but is it full or is it partial? To me I would consider this a partial (or broken) white collar. It extends from shoulder to shoulder, however there are some gaps in it. To me white shoulders is along the same line as white wings, significantly less white, but still present. So for me I personally think to myself (although you are all free to disagree) when there is 60% or more white collar present, it is a partial or a broken white collar. When it is complete, it is just a white collar.