Asteria tends to have black hair in my mind and blue-green eyes. After all, with Draco and his entire family being blond, it's not necessary for Asteria to be blond as well for Scorpius to be. (Though it's definitely possibly she is!)
Also, I tend to favor the Asteria spelling of her name because that's how JKR spelled it on the Weasley family tree. While Astoria does sound so much more posh, I like Asteria better because of how it fits in with the other names in the Greengrass-Malfoy family. It's from Greek Mythology like Daphne, Draco and Scorpius and means "starry". Asteria was a Titan like Hyperion (Scorpius' middle name) and the goddess of astrology and necromancy. And like Narcissa, it's a floral name! Narcissa being after the narcissus flower and Asteria being after the aster flower.
Anywho. My Asteria tends to be pretty different from most versions of Asteria out there. However, like most people in this thread, I see her as being in Slytherin. It's also pretty popular to have her in Ravenclaw but I've yet to see a Hufflepuff or Gryffindor Asteria.
I see Asteria as getting along well with Daphne, moreso as they've grown older than when they were younger.