Have you read the actual SOP description? In the physical book?
If you have, please tell me what it does say about leg color.
I have not (don't care enough to pay the usual high price.)
But if I am trying to track it down from other sources, I find things like this:
McMurray sells "Blue Ameraucana," that are supposed to meet the actual APA standards. They list leg color as "slate."
https://www.mcmurrayhatchery.com/blue-ameraucana.html
Wikipedia says slate legs on all varieties, and gives their source as Storey's Illustrated Guide to Poultry Breeds.
https://en.wikipedia.org/wiki/Ameraucana
I've read some of the threads on this site, discussing breeding of Ameraucanas to SOP. They all want slate legs.
It is very clear from all sources that I can find, that Ameraucanas of all recognized or project varieties are supposed to have slate legs. So I do not know how "bad" non-slate legs may be (a disqualification, or a fault, or just not the preferred color), but I sure don't see anyone encouraging or trying to breed for any non-slate color.
As I was looking for information, I kept noticing that Araucanas in the US (the tufted breed with no tails) are supoosed to have yellow skin. I do not know whether the skin color difference is deliberate, to make them easier to tell apart, or if there is some other reason for it.
As regards McMurray's "Ameraucanas" that are a mix of colors, I can see why they want to keep calling them that, since they were using the name before the breed was admitted by the APA. But they are not breeding to the existing standard, so for discussions of what the standard is, the leg color of their birds is irrelevant.