I'll try and stick to the coloring here, since it looks like someone else did the lines.

The color scheme looks nice overall. You've kept it simple and the colors go well together and don't clash.

For some suggestions--

First, the coloring is really flat, as there is no shading or variance of tone. I don't know what kind of range of colors you have to work with. But even coloring in an area really lightly, and then coloring with more pressure on the pencil where the shadows can be will help create some depth. Layering colors is also a good way to create volume. You did it a bit in the background where a few colors overlap. Some colored pencils don't blend all that well, but you can try things like crosshatching.
Here's a good crosshatching and a good blending/layering tutorial:
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Hope this helps!