The Yellow and green look great together. You can find plenty of sports teams with that combo as well, so it's a popular color scheme.
And the simplicity of the uniform is another part of what makes it great, just the form fitting tights, jacket and belt.
It looks so much better than many of her other uniforms that have all of the extra nonsensical items like the hood, tunic, and especially the scarf (I hated that thing)