It is not the print bed side that you're seeing. It's also a fairly close up pic, and then I cropped out more. The lines aren't as prominent in person at arms length.

The print bed side is nice and smooth and looks better than this. I had a couple of minor issues getting this printed that also contributed to the top layers not looking their absolute best, but even if they did, you would still be seeing the print lines. There's not a lot that can be done about that. 3D printing is a prototyping technology, after all.

What I did here was to make the white rectangle the first color (Esun PLA+ Cool White), then at a certain layer height - I think 2mm - I unloaded the white filament, swapped to a blue silk filament and resumed the print. So all the blue you see is sitting on top of the white.

Some people have printers that can automatically swap between filaments, and therefore they can "paint" prints like this to be the full yellow, blue, white and black that you see elsewhere. Those can be expensive and hard to operate though, so I don't own one. I sure would like that capability though.