well, Balou certainly was helped by his sire Baloubet. The dam’s damsire had white as well - Domino. It once it comes through enough generations, the cumulative effect can increase, until you get stallions - Balou, Baloubet - who are high color producers.
ATLANTUS VAN DE ROSHOEVE
http://www.paardenfokken.nl/pedigree.php?horseid=508800
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Heartbreaker had enough white, contributed no doubt in part by Nimmerdor, though he was more minimal (which doesn’t mean a whole lot when it comes to black-based colors, it just gets more exciting in terms of “he’s got it” when you see more white on the black-based colors). His damsire, President/Titan, is another black based horse with white. So, it was another case most likely of the white ending up concentrating.
[quote=littleum;5570489]My post references how overo was understood 20 years ago. It was believed there was a single Overo gene and that it was dominant recessive (o/o)
My post is accurate about the inaccuracy. 
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I gotcha! 