I have about the same feelings on this as does GenaLeah. Spring looks very well rendered but winter does stick out more and take away from her. Now granted I had this happen FAR to many times to myself. When you were doing this it could have looked fine with the image sitting right in front of you. But sadly scanners 99.9% of the time kill images ><. Evil technology but it happens to the best of us. Other then that I love how winter looks like he has ice sticking on him. Your control of your markers is very nice.

Myself I have taken all of my colors, made swatches on paper and scanned it to get an idea of how it looks in the digital world. That could help you so that your colors don't stick out so much drawing away from one another next time.

~Rizyu~

(Alright, this is my first critique I've ever written so it's probably not going to be too amazing...)
First I'll start with one of the positives, the biggest thing I love in this is the texture. It's exhibited in all parts of the piece, in the smooth vs sharp lines, the techniques used in the coloring, and the high contrast shading compared to smooth shading. Everything on Spring's body looks satin and velvety, while Winter's coat looks like a smooth but firm fabric and his ice-hair just has a great effect that makes it look like pure glass.
The biggest downfall to this picture is in the color, not ALL of the color, just in parts. But most of all my peeve lies within Spring's skin. Though I feel it is a bit unfair to be criticizing the color choice of a character I've rarely seen (meaning that there's probably a very good reason for this color and it's supposed to be that way, I just don't know about it), but nevertheless I feel like I have to comment on how it affects the drawing. The color is incredibly distracting, somehow it doesn't blend into the cool colors like the rest of his outfit does, instead it catches attention in an unpleasant way. There's almost too much of the color there, though I'm not saying color is a bad thing!! But it just doesn't blend with the rest of his outfit, I think it would've benefited if it had been done a slightly lighter tone. In contrast, Winter's very colorful blue skin is able to blend with his design perfectly, somehow fitting with both of the different shades of blue on his shirt and jacket, and with his hair, of course.
There's only two more nit-picky things I have to mention, one being the jagged light-blue formation around Spring's head, which I assumed is part of Winter's outfit. It's a little hard to tell what it is or if it IS a part of Winter's outfit at all. The other thing is the fade effect at the bottom, it's problem is that it doesn't seem to fade, instead it looks as if they're standing behind some blobby shape that is the same color as the back ground. It could have been done more efficiently and in a more visually pleasing way that could have helped the picture, there's a million ways a fade can help enhance the mood, setting, or style of the drawing; but this one doesn't seem right for this image.

Sorry I seem like such a negative force here, this really is a fantastic image, it is very skillfully done, and as always your style is very pleasing to look at and structurally makes sense!! (A problem I very often run into in my own style and drawings...) You should really feel good about this piece, the interaction between the characters is very cute and the whole thing is very beautifully done. I truthfully wish my own art can be this great someday!
Anyway, I hope this critique was useful!! It seems kind of weird to be giving advice to artists I consider much more skilled than myself, but hopefully I can be helpful in some way.

Great work, and best of luck in your future projects!!
-GenaLeah