User blog comment:Blakebellabootyy/Emerald's Semblance/@comment-25396609-20160109051339/@comment-4010415-20160111162229

Yeah, but we choose to call Emerald's Semblance hallucinations because she can only cause specific targets to see something that isn't there, rather than generating an illusion that everyone in the area can see.

Emerald targets someone and makes their mind interpret what the eyes are seeing wrongly.

Neo seems to bend the light to make it look like something is there, and everyone's eyes see that manipulated light. For example, to make it look like her eyes are green, she just makes it to where only green light bounces off of her eyes to other people's eyes. Rather than manipulating how their brains interpret it, she manipulates what the eyes are able to see.

So, it's really a difference between Emerald affecting the mind and Neo affecting the eyes.