There is no way to make you harder to see on the astral beyond increasing background count, which isn't easy to do if you're trying to avoid drawing attention to yourself in the first place. There's no way to just make yourself astrally invisible, sadly.
This can make a mage the bane of stealth builds as astral perception is not a visual sense, and so isn't affected by common modifiers like darkness, meaning it's tougher to sneak past them. However, the book does say an Assensing test is needed if someone is trying to actively hide from you, so it doesn't mean they automatically find you.
Also worth noting, Manascape changes what your aura looks like, but you're still clearly a living thing-- Manascape can't remove your aura, and objects like drones don't have auras (so you can't pretend to be a cardboard box on the astral).