It certainly makes it easier to photograph, or at least to find with the autofocus.

There are also two color blemishes on the top surface which I'm a little miffed about, since these were defects directly in the spool of filament. It must have been made with like two pellets of the wrong stuff in the hopper.

Oh well. It's a tool, it's not like I'm hanging it up on the wall in a frame or something.

Yeah, the grey looks great. Just the right ammount, imo.

I can't speak for other printers, but my X-Max 3 has an absurdly thick aluminum plate under there which seems to spread the heat pretty well. I've poked it with my little IR camera and it's not 100% even but it's not bad. The only side effect of this is that it takes a month of Sundays to fully reach temperature, especially when you're aiming for higher temperature materials like ABS.

Here it is on today's preheat for PLA:

(IR cat tax paid here.)

A cooler bed can prevent warping. But a warmer bed may be better for overall plate adhesion.

now i would really like to try a 256 mm³ cube

That's a cube measuring ~6.5mm x 6.5mm x 6.5mm...I know the A1 is small, but that seems fairly unambitious.

I think the yellowish part is just a shadow from something, because the 'remove screws' stickers on the sides also change color

That's just the shadow cast by the gantry blocking the LEDs that are all arranged along the front edge of the machine.

Rather, I have two of these which are just tiny specs of grey or black or grey or something, which got printed right into the top surfaces. They're small, but annoyingly visible. This is what I get for buying cheap filament, possibly.

Exactly so.