With my comment about the light, I was actually thinking more about the vertical position. Is the light coming from above, or below? The top of the base is lit, but the top of the column is in shadow. You have some highlights in the middle of the column, but what's creating them?
A centre light source (same amount of shadows on the left/right) is a little dull, but it's physically plausible xP
This is the tangent I was referring to:

That colour boundary and the top of the column align almost perfectly, making it feel like the pillar is contained within the darker blues, and the lighter blue is a separate object on top. It's generally a good idea to keep boundaries away from any other boundaries, unless they're almost perpendicular. When a shape overlaps another shape, it should do so decisively, try to avoid slight, ambiguous overlaps.
Even though the sky is a single object, the individual colours still form their own shapes, and if these shapes interact with other shapes in weird ways (e.g. tangents), that can cause the sky to read as a bunch of different objects rather than as a single gradient object.