I don't think you need a dedicated AA colour, you could use your darker blue and purple. For AA, the hue barely matters. Here's a partial edit.
Alternatively, since you have internal outlines, maybe you could extend the external dark AA into an external outline.
Probably a easy fix when just making a dedicated AA color.
The external AA looks weird on a light background, but on a dark background, the dark parts of the sprite would be lost. Perhaps AA meant for this lighter background would be better?
Hmmm..