Chad, I'm afraid to answer about "specials" because it could start a debate which would be very off-topic. I guess I can break it into a separate thread if we get too far afield.
To the best of my understanding, Akro didn't make any style that they specifically called "Special". That is a collector's name. Dark outline of the sort which is a relatively common byproduct of multicolor marble manufacture doesn't change what Akro intended. It might indeed get some collectors to call it a Special, but generally not me.
If Akro ran the marble in their standard two-color Prize Name run and it got an additional thin stream of dark glass on the borders of the main colors that didn't stop it from being a Prize Name. Also, here's a good time to say Bruce is right about white or gray or cream or whatnot being counted as one of the two colors. But I don't know how non-white a white-ish shade would need to be for people to think of it as "non-white". In the blue/gray one that I think you're talking about, Sara, I'm seeing it as still in the blue/white region. As one last side note, I note that the colors didn't have to be strictly opaque ... some transparency slipped into some the ribbons of some marbles in Prize Name runs but the overall effect was still an opaque marble and that was apparently good enough for Akro.
Akro named their intentional three-color version "Tri-Color Agate".
"Special" is one of those names like "Ace" which early collectors saw on boxes or something and made conclusions about but the conclusions turned out to not quite match what Akro meant (or what Akro probably, in my opinion, meant). Akro sold assortments in boxes marked Special. They advertised Sparklers as one of the things you might get in a Special Assortment. And they had various other marbles including popeyes in the Special section of their salesman sample box.