Where/why did Herda come into play? Has nothing to do with the color of this colt and his grey foot.

Grey is not a "color" To put it simply, it covers over what the horse's true color is. A horse can be any color under the grey, and coat pattern too will often hide. The roaning foot (as it isn't "greying" it's roaning), wouldn't be at all surprised if there was a sabino gene in play there. As for turning grey, the mare would have had to be homozygous grey (true color could be anything remember) and her offspring would be 100% grey. She wasn't, as your colt proves, so she had a 50% chance of throwing the grey. That's just a real basic breakdown of how grey works :)
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...May The Horse Be With You...
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