When it comes to that race thing, of course there's the blindly discriminatory. There's also the blindly naive. Crossing an empty street because there's a group of very thug-looking people in your is something you're going to do unless you feel really safe somehow - or are armed yourself.
This is just one of the things that comes along with dealing with the unfamiliar. Personally, in my life in a city, I try to be as trusting as I can allow myself, of anyone I meet. But I know that a mugging or worse could happen in an instant.
You do know that even you discriminate every day, right? That is is actually human to do so? It's wrongful, or codified, or systemic discrimination that tends to make things worse. Especially when it brings on passion or fury that is logically unwarranted.
As survival becomes less important to a society (as bad things can be for people in say North America, its still usually a far cry from other regions), yes, they'll opt more for trust. But that doesn't remove the baser instinct that will opt for the familiar (even in such stupid to rely on terms like 'race') for the sake of survival. Like with like, like forms community/family with like, like keeps other like safe and destroys unlike. Grunt grunt. Keeps you alive longer in some simple ways, but in a place where that's less important, it looks primitive. And it is. But it also speaks to a truth. Life is complicated. :S
~~~
Wrongful discrimination also feeds on conflict or isolation. In order for Ashley to keep considering herself so correct, the Alliance would have had to segregate itself from the Citadel species, or gone to war with the Turians or something like that. Then, she'd be justified.
But over time, positive interactions with aliens had to happen. We know she has them behind the scenes and in places like elevators and in combat in ME1. She sticks with the Alliance but despises human-supremacy in ME2. She takes on the role of Spectre and regardless of hardening/non-hardening in ME1, she has a more positive view of aliens in ME3, to the point of protecting the Council from threats (regardless of Udina being there - she hates Udina too anyway).
This is why she's wearing the blue. Having learned more, she has become a protector of the many, even if a more blunt form of one compared to Kaidan. As a result though, her resolve about the world becomes more muddled, and she has to decide to stick to her new role of protecting all of the Council, in her new role as protector... or stick to the familiar ("You know me") Shepard (who can sometimes be in red armor, red eyes, Renegade, and is human-centric himself).
That was the Citadel coup - or at least the better aspects of it. Ashley had good but uninformed points in ME1, retreated into the familiar but in a softened way in ME2, and stood up in acceptance of aliens in ME3 - if only for the sake of the war effort.