"Elle est aussi rouge qu'une tomate."

Translation: She is as red as a tomato.

[ChristaSantos]

"She is red as a tomato?" will work?

[Wanda655505]

Why can't one say, "Elle est rouge comme une tomate," ?

[jolynnedougherty]

Revisiting this. Why is the aussi necessary? Is that part of the subjunctive?

[weavboo]

Aussi is used to indicate equality, pretty much like "as much as". Examples: J'ai aussi faim que toi = I'm as much hungry as you.
Nous avous tous aussi faim = We are all as much hungry

It can also be a synonym of également (=one of the possible meaning of "too"), although "aussi" is a bit more usual in everyday situation. Example : Toi aussi? = You too?

There is no subjunctive here, don't think "que" is necessarily linked with subjunctive, it can also mean other things, which I would not be able to explain simply. For our case here, "Aussi ... que" = "As much ... as"