What a wonderful work of art you did! The colors on these two are absolutely vivid and it really makes them pop out which makes them look all the more appealing.
I know Fluttershy and Rainbow Dash are on clouds so background look really good together with them. It's simplistic enough to add to the overall picture but isn't too much that it interferes with the main focus which is Fluttershy and Rainbow Dash. Also on a side note the the drawings in the background is a nice touch to it.
Onto the two pegasi themselves, the style you used to draw them is absolutely beautiful. They look so cute together so it only adds to the charm of the impact. Their original design was cute but you went and made it even cuter. Even the eyes look pretty darn lovely with the little glow they have in them. I also admire the posture you did them in. They both look so cute it's almost overwhelming.
In my conclusion, I love just about everything about this, from the colors to the shading to the anatomy. I believe this is a really well done!
Rainbow Dash and Fluttershy are both one of my favorites. I think that this is a lovely picture you did here. The eyes defiantly caught MY eye because I've never seen anything like it. Normally, the my little pony eyes would have a black in the middle...but instead you made yur orginal and you should be VERY proud of that. I also like the stance that they both have. RD is lying on a belly (Probable going to draw something extreme) drawing away whilst Fluttershy is just about finished. The sading is a nice touch also. I can easily tell that the sunlight is coming from the right hand side. Most artist don't take much care when making shadings. SO WELL DONE FORE THAT!
In short, this is a very beautiful,lovely,nice,sweet and AWESOME piece of work and I hope you make loads of these in the future.