Nice composition! The sunlight catching Fluttershy like a golden arrow, leading to RD who's (momentarily at least!) just incredibly proud of her friend's reserves of determination. You go, champ! I assume the contrail up on high is a symbol of aspiration?

The shading on Rainbow Dash looks a bit inconsistent. It took me a second or two to figure out her right haunch wasn't sky. It's a contrast thing: compared to her left buttcheek, the right one looks very different. Consider how it'd look with a flatter, lighter top before her tailbone, and shading into the shadow along her neck/withers. I'd also suggest having a critical comparison at her face and body shading and seeing where they agree and disagree, asking where they're telling you the light source is.

(Caption aside, I always figure Dashie's self-congratulatory facade is something of a defence mechanism, so it's nice to see her with shields down for two seconds, but still having her own strength of character and the honesty to admire what her friend has achieved (awww!). It's a contrast of extra depths the two characters are finding in themselves, and I think this piece captures that theme very nicely overall.)

This is very beautiful work. i like how the colors are displayed in this drawing.
the shading is fantastic
and dont get me started on the hair omg AMAZING!!!