I absolutely adore this and the scarf just makes this the greatest thing ever please inject it directly into my veins
First and foremost, the background is super easy on the eyesi, your attention to detail on the clouds, the sun, and the colors are superb. The colors of the sky make it seem like it could either be very early morning or early evening, which is neato that it's open to interpretation.
The mostly cool toned shading helps emphasize that it's a colder setting, what with her scarf and the overcast skies. Your shading is also very soft, which works really well with ponies.
But your soft shading causes a few minor problems, particularly in nooks and crannies. The softer the shading, the less definition there is, particularly in the area of her shoulder, belly and flank (the area between the hind leg and belly - not the butt, as MLP erroneously refers to that area as!) The soft shading from in front of her shoulder and behind it sort of run together. Since I found it hard to explain, I did some tweaking for a side by side comparison to show what I mean: [link] (touch up on the left, original on the right)
So by neatening the placement of your shadows a little you can define her shoulder and show the slight roundness of her little pony tummy, while still staying true to your light source, and everything flows a little better!
Her eyes are really pretty, I love how they're the brightest thing in the picture. But a little minor detail, to me, they look just slightly off. Normally the rule of thumb is whites showing above the eyes indicates madness/insanity, or being on edge. Whites showing below the eyes indicates (for lack of a better word) dopeyness, as well as friendliness. Now that might be a little too hypercritical for a highly stylized drawing and it's entirely a matter of opinion. But I think dropping her upper lids slightly and defining her 'lash' line to a thicker line would give her a better expression of curiosity and innocence without looking startled. Tiny details go a long ways.
I love how you did her wing, but I think the second one should be showing at least a little bit! I actually didn't notice it until looking it over before finishing this. So it might have been one of those things that you totally forget without meaning to.
Keep on doing what you do, you are fabulous with mimicking traditional styles in digital programs. You're also really fucking great at backgrounds, which doesn't go for a lot of people! And as I stated before, I really wanna see the stuff you made before MLP:FIM!!

Being a big fan of My Little Pony, I always love to see different interpretations of the wonderful characters in the series.

Especially Fluttershy, who I can definitely call my favourite! I love how you captured her "wide-eyed wonder" look with such depth and three dimentionality.

The colours made me think of marshmallow and cotton candy, and I truly love how you blended the clouds to make it look cold.

One thing that might need attention (although very little!!) though, is the consistancy in hair texture on the left and the right.

Last word: Well done! Your technique is beautiful and enchanting, creates the nostalgic feel. Hope you never stop creating!