HGG Community Forums

Here's a list someone compiled late last year. :)
http://hj2.huntandjump.com/forum/discussion/4925/special-dhh-list#Item_24

I'm pretty sure any Rank Special horses are Perfect Foundations. :)

Hidden, as Rose said, all rank specials are perfect foundations (even if they are described as exceptional in their blurb--that only applies to HJ1, not this version of the game!).

In addition to being Perfect Foundations, rank specials usually have a specific combination of base color and pattern. Often the colors or patterns are rare, like Sabino or pearl. Sometimes otherwise lethal combinations are present, like horses that are homozygous for frame. Sometimes the color is spelled out in the description and sometimes it is a surprise. Some rank specials have every single gene controlled (like Shades of Pale, which are heterozygous for everything) while others have a base controlled but may have extras (my Yule Log stallion is a brown Rabicano brindle like everyone else's but he also carries tobiano as a bonus).

Rank Specials can come up in your random daily herd helper very rarely, but most of them come from game-wide "gift" herd helpers from Ammit on special days. One of those is coming up tomorrow when we will (hopefully) all get Freaky Friday herd helpers for Friday the 13th.