OK
Top left is your file and although on my setup it was difficult without the proper retraction settings and slight over extrusion it turned out fine.
Bottom left is my file and I have intentionally under extruded for this example. You'll have to ignore the color bleed on both left photos.
Bottom right was printed with 0 top fill layer with a layer of black just under the yellow to help highlight the affect.
Top Right was printed with 1 top fill layer with a later of Yellow just under the Black. Notice yo don't see any yellow showing through? I also am under extruding (same extrusion multiplier settings) as I did for the top right print.

Thoughts:
You probably need to increase your extrusion multiplier slightly. Since using your file I was over extruding we can eliminate extrusion width.
Try slightly higher temps.
locate and remedy any source of slop or play in the mechanical side of things.
I will print one more of these with the proper extrusion multiplier just to see if I can get that smooth finish you are hoping for.
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