… colorless card with a gold border

@Phil Srobeighn  
Yeah, I to be a much more flavor guy, so I tend towards top-down design. That said I am willing to compromise with other peoples ideas, as you saw here. That said, if we were to make a cycle of cards about the main six, their complex enough characters that pinning them down to a single color would be difficult. They would most likely be two or three color cards.

@Rikmach  
I like all those options. In the end, you are right, she is more blue than anything. I just think bottom-up more than top-down when I think of card design, so I want to fit somepony from the Mane Six into colorless to have a six-color cycle in a hypothetical block, especially now that we have Wastes, and I think for that abnormality that is colorless it’s Twilight or Pinkie Pie.

@Phil Srobeighn
 
Hmmm. Are you suggesting she transcends color because her talent is magic? I can kinda see that, but that suggests more Multicolored than Colorless. Maybe we can make her something like The Reaper King (Which is technically all and no colors). Though I’m not sure if that evades the Commander rule issue. Maybe have her have a special rule such as “Twilight counts as having only the same colors as her commander”?
 
Also, while I can see your perspective on color issues, she still, as a character, has a strong Blue identity (though she also has a white streak that’s been getting stronger), so maybe have a blue activated ability?

@Rikmach  
She trancends color and is ageless (even if she is young). She is the essence of both pure force of magic and of friendship, which means she should be accessable to a Planeswalker of any color alignment. If any if her friends if any color were a commander, she should not be barred from being in their deck based on color identity.

@Phil Srobeighn  
How exactly to you justify a colorless Twilight? Her motives and behaviors are extremely blue, and the only colorless creatures in magic are either artifacts (who usually lack the sapiance or nature to acquire a color identity) and ancient, timeless horrors (who predate and transcend color), or things that artificially had their color identity scoured from them. How does Twilight fit into any of these categories, or otherwise separate herself from her apparent color identity?

I watched Finding Dory last weekend. My wife really liked the “What Would Dory Do?” conversation. For those of you who haven’t seen it, it goes something like this:
 
Marlin: What would Dory do? She would observe her surroundings, analyze the situation, weigh her options-  
Nemo: Dad, that’s what Marlin would do.  
Marlin: You’re right! She wouldn’t even think about it! She would just go with the first thing she saw!
 
It is this quality that Dory has that Marlin doesn’t that helps defines Haste. Dory is Legendary Creature - Fish: Haste.  
_{“At the beginning of each upkeep, shuffle your hand into your library, then draw that many cards.” But that’s not important right now.}
 
What is it about Twilight Sparkle that makes you think Haste? I can only think of one instance where Twilight did something without thinking about it, come to think of it…
 
Twilight Sparkle  
Legendary Creature - Unicorn Wizard  
Twilight Sparkle enters the battlefield tapped.  
If Twilight gains haste, exile it. Return it to the battlefield transformed at the beginning of the end step.  
“I cast the spell so I could find out what it was, but nothing seemed to happen.”
 
Princess Twilight Sparkle  
Legendary Creature - Alicorn Lord  
Flying
 
This being said, I have long been a supporter of a colorless Twilight Sparkle, so I am glad to see someone else take it up.

Okay, first point: The card has no colour in its cost, but the border is gold, which denotes multicolour.  
Second: The activated ability should read “Twilight Sparkle gains protection from the creature type of your choice until end of turn.”  
Third: The reminder text for the activated ability is unnecessary, as all activated abilities can be activated at instant-speed unless noted otherwise.
 
Those are the only mechanical/formatting issues I can spot.  
As for flavour issues: